diff --git a/db/builder.cc b/db/builder.cc
index 729f9fd..5fa405d 100644
--- a/db/builder.cc
+++ b/db/builder.cc
@@ -56,7 +56,7 @@ Status BuildTable(const std::string& dbname,
       s = file->Close();
     }
     delete file;
-    file = NULL;
+    file = nullptr;
 
     if (s.ok()) {
       // Verify that the table is usable
diff --git a/db/c.cc b/db/c.cc
index 0ccf08c..77b33d5 100644
--- a/db/c.cc
+++ b/db/c.cc
@@ -129,10 +129,10 @@ struct leveldb_env_t {
 };
 
 static bool SaveError(char** errptr, const Status& s) {
-  assert(errptr != NULL);
+  assert(errptr != nullptr);
   if (s.ok()) {
     return false;
-  } else if (*errptr == NULL) {
+  } else if (*errptr == nullptr) {
     *errptr = strdup(s.ToString().c_str());
   } else {
     // TODO(sanjay): Merge with existing error?
@@ -154,7 +154,7 @@ leveldb_t* leveldb_open(
     char** errptr) {
   DB* db;
   if (SaveError(errptr, DB::Open(options->rep, std::string(name), &db))) {
-    return NULL;
+    return nullptr;
   }
   leveldb_t* result = new leveldb_t;
   result->rep = db;
@@ -199,7 +199,7 @@ char* leveldb_get(
     const char* key, size_t keylen,
     size_t* vallen,
     char** errptr) {
-  char* result = NULL;
+  char* result = nullptr;
   std::string tmp;
   Status s = db->rep->Get(options->rep, Slice(key, keylen), &tmp);
   if (s.ok()) {
@@ -244,7 +244,7 @@ char* leveldb_property_value(
     // We use strdup() since we expect human readable output.
     return strdup(tmp.c_str());
   } else {
-    return NULL;
+    return nullptr;
   }
 }
 
@@ -269,9 +269,9 @@ void leveldb_compact_range(
     const char* limit_key, size_t limit_key_len) {
   Slice a, b;
   db->rep->CompactRange(
-      // Pass NULL Slice if corresponding "const char*" is NULL
-      (start_key ? (a = Slice(start_key, start_key_len), &a) : NULL),
-      (limit_key ? (b = Slice(limit_key, limit_key_len), &b) : NULL));
+      // Pass null Slice if corresponding "const char*" is null
+      (start_key ? (a = Slice(start_key, start_key_len), &a) : nullptr),
+      (limit_key ? (b = Slice(limit_key, limit_key_len), &b) : nullptr));
 }
 
 void leveldb_destroy_db(
@@ -418,11 +418,11 @@ void leveldb_options_set_paranoid_checks(
 }
 
 void leveldb_options_set_env(leveldb_options_t* opt, leveldb_env_t* env) {
-  opt->rep.env = (env ? env->rep : NULL);
+  opt->rep.env = (env ? env->rep : nullptr);
 }
 
 void leveldb_options_set_info_log(leveldb_options_t* opt, leveldb_logger_t* l) {
-  opt->rep.info_log = (l ? l->rep : NULL);
+  opt->rep.info_log = (l ? l->rep : nullptr);
 }
 
 void leveldb_options_set_write_buffer_size(leveldb_options_t* opt, size_t s) {
@@ -517,7 +517,7 @@ leveldb_filterpolicy_t* leveldb_filterpolicy_create_bloom(int bits_per_key) {
   };
   Wrapper* wrapper = new Wrapper;
   wrapper->rep_ = NewBloomFilterPolicy(bits_per_key);
-  wrapper->state_ = NULL;
+  wrapper->state_ = nullptr;
   wrapper->destructor_ = &Wrapper::DoNothing;
   return wrapper;
 }
@@ -544,7 +544,7 @@ void leveldb_readoptions_set_fill_cache(
 void leveldb_readoptions_set_snapshot(
     leveldb_readoptions_t* opt,
     const leveldb_snapshot_t* snap) {
-  opt->rep.snapshot = (snap ? snap->rep : NULL);
+  opt->rep.snapshot = (snap ? snap->rep : nullptr);
 }
 
 leveldb_writeoptions_t* leveldb_writeoptions_create() {
@@ -586,7 +586,7 @@ void leveldb_env_destroy(leveldb_env_t* env) {
 char* leveldb_env_get_test_directory(leveldb_env_t* env) {
   std::string result;
   if (!env->rep->GetTestDirectory(&result).ok()) {
-    return NULL;
+    return nullptr;
   }
 
   char* buffer = static_cast<char*>(malloc(result.size() + 1));
diff --git a/db/corruption_test.cc b/db/corruption_test.cc
index 37a484d..0b93c24 100644
--- a/db/corruption_test.cc
+++ b/db/corruption_test.cc
@@ -39,7 +39,7 @@ class CorruptionTest {
     dbname_ = test::TmpDir() + "/corruption_test";
     DestroyDB(dbname_, options_);
 
-    db_ = NULL;
+    db_ = nullptr;
     options_.create_if_missing = true;
     Reopen();
     options_.create_if_missing = false;
@@ -53,7 +53,7 @@ class CorruptionTest {
 
   Status TryReopen() {
     delete db_;
-    db_ = NULL;
+    db_ = nullptr;
     return DB::Open(options_, dbname_, &db_);
   }
 
@@ -63,7 +63,7 @@ class CorruptionTest {
 
   void RepairDB() {
     delete db_;
-    db_ = NULL;
+    db_ = nullptr;
     ASSERT_OK(::leveldb::RepairDB(dbname_, options_));
   }
 
@@ -237,8 +237,8 @@ TEST(CorruptionTest, TableFile) {
   Build(100);
   DBImpl* dbi = reinterpret_cast<DBImpl*>(db_);
   dbi->TEST_CompactMemTable();
-  dbi->TEST_CompactRange(0, NULL, NULL);
-  dbi->TEST_CompactRange(1, NULL, NULL);
+  dbi->TEST_CompactRange(0, nullptr, nullptr);
+  dbi->TEST_CompactRange(1, nullptr, nullptr);
 
   Corrupt(kTableFile, 100, 1);
   Check(90, 99);
@@ -251,8 +251,8 @@ TEST(CorruptionTest, TableFileRepair) {
   Build(100);
   DBImpl* dbi = reinterpret_cast<DBImpl*>(db_);
   dbi->TEST_CompactMemTable();
-  dbi->TEST_CompactRange(0, NULL, NULL);
-  dbi->TEST_CompactRange(1, NULL, NULL);
+  dbi->TEST_CompactRange(0, nullptr, nullptr);
+  dbi->TEST_CompactRange(1, nullptr, nullptr);
 
   Corrupt(kTableFile, 100, 1);
   RepairDB();
@@ -302,7 +302,7 @@ TEST(CorruptionTest, CorruptedDescriptor) {
   ASSERT_OK(db_->Put(WriteOptions(), "foo", "hello"));
   DBImpl* dbi = reinterpret_cast<DBImpl*>(db_);
   dbi->TEST_CompactMemTable();
-  dbi->TEST_CompactRange(0, NULL, NULL);
+  dbi->TEST_CompactRange(0, nullptr, nullptr);
 
   Corrupt(kDescriptorFile, 0, 1000);
   Status s = TryReopen();
@@ -343,7 +343,7 @@ TEST(CorruptionTest, CompactionInputErrorParanoid) {
     Corrupt(kTableFile, 100, 1);
     env_.SleepForMicroseconds(100000);
   }
-  dbi->CompactRange(NULL, NULL);
+  dbi->CompactRange(nullptr, nullptr);
 
   // Write must fail because of corrupted table
   std::string tmp1, tmp2;
diff --git a/db/db_bench.cc b/db/db_bench.cc
index 701b128..115cf45 100644
--- a/db/db_bench.cc
+++ b/db/db_bench.cc
@@ -111,12 +111,12 @@ static bool FLAGS_use_existing_db = false;
 static bool FLAGS_reuse_logs = false;
 
 // Use the db with the following name.
-static const char* FLAGS_db = NULL;
+static const char* FLAGS_db = nullptr;
 
 namespace leveldb {
 
 namespace {
-leveldb::Env* g_env = NULL;
+leveldb::Env* g_env = nullptr;
 
 // Helper for quickly generating random data.
 class RandomGenerator {
@@ -370,18 +370,18 @@ class Benchmark {
             kMajorVersion, kMinorVersion);
 
 #if defined(__linux)
-    time_t now = time(NULL);
+    time_t now = time(nullptr);
     fprintf(stderr, "Date:       %s", ctime(&now));  // ctime() adds newline
 
     FILE* cpuinfo = fopen("/proc/cpuinfo", "r");
-    if (cpuinfo != NULL) {
+    if (cpuinfo != nullptr) {
       char line[1000];
       int num_cpus = 0;
       std::string cpu_type;
       std::string cache_size;
-      while (fgets(line, sizeof(line), cpuinfo) != NULL) {
+      while (fgets(line, sizeof(line), cpuinfo) != nullptr) {
         const char* sep = strchr(line, ':');
-        if (sep == NULL) {
+        if (sep == nullptr) {
           continue;
         }
         Slice key = TrimSpace(Slice(line, sep - 1 - line));
@@ -402,11 +402,11 @@ class Benchmark {
 
  public:
   Benchmark()
-  : cache_(FLAGS_cache_size >= 0 ? NewLRUCache(FLAGS_cache_size) : NULL),
+  : cache_(FLAGS_cache_size >= 0 ? NewLRUCache(FLAGS_cache_size) : nullptr),
     filter_policy_(FLAGS_bloom_bits >= 0
                    ? NewBloomFilterPolicy(FLAGS_bloom_bits)
-                   : NULL),
-    db_(NULL),
+                   : nullptr),
+    db_(nullptr),
     num_(FLAGS_num),
     value_size_(FLAGS_value_size),
     entries_per_batch_(1),
@@ -435,12 +435,12 @@ class Benchmark {
     Open();
 
     const char* benchmarks = FLAGS_benchmarks;
-    while (benchmarks != NULL) {
+    while (benchmarks != nullptr) {
       const char* sep = strchr(benchmarks, ',');
       Slice name;
-      if (sep == NULL) {
+      if (sep == nullptr) {
         name = benchmarks;
-        benchmarks = NULL;
+        benchmarks = nullptr;
       } else {
         name = Slice(benchmarks, sep - benchmarks);
         benchmarks = sep + 1;
@@ -453,7 +453,7 @@ class Benchmark {
       entries_per_batch_ = 1;
       write_options_ = WriteOptions();
 
-      void (Benchmark::*method)(ThreadState*) = NULL;
+      void (Benchmark::*method)(ThreadState*) = nullptr;
       bool fresh_db = false;
       int num_threads = FLAGS_threads;
 
@@ -532,16 +532,16 @@ class Benchmark {
         if (FLAGS_use_existing_db) {
           fprintf(stdout, "%-12s : skipped (--use_existing_db is true)\n",
                   name.ToString().c_str());
-          method = NULL;
+          method = nullptr;
         } else {
           delete db_;
-          db_ = NULL;
+          db_ = nullptr;
           DestroyDB(FLAGS_db, Options());
           Open();
         }
       }
 
-      if (method != NULL) {
+      if (method != nullptr) {
         RunBenchmark(num_threads, name, method);
       }
     }
@@ -643,7 +643,7 @@ class Benchmark {
     int dummy;
     port::AtomicPointer ap(&dummy);
     int count = 0;
-    void *ptr = NULL;
+    void *ptr = nullptr;
     thread->stats.AddMessage("(each op is 1000 loads)");
     while (count < 100000) {
       for (int i = 0; i < 1000; i++) {
@@ -652,7 +652,7 @@ class Benchmark {
       count++;
       thread->stats.FinishedSingleOp();
     }
-    if (ptr == NULL) exit(1); // Disable unused variable warning.
+    if (ptr == nullptr) exit(1); // Disable unused variable warning.
   }
 
   void SnappyCompress(ThreadState* thread) {
@@ -703,7 +703,7 @@ class Benchmark {
   }
 
   void Open() {
-    assert(db_ == NULL);
+    assert(db_ == nullptr);
     Options options;
     options.env = g_env;
     options.create_if_missing = !FLAGS_use_existing_db;
@@ -914,7 +914,7 @@ class Benchmark {
   }
 
   void Compact(ThreadState* thread) {
-    db_->CompactRange(NULL, NULL);
+    db_->CompactRange(nullptr, nullptr);
   }
 
   void PrintStats(const char* key) {
@@ -1004,7 +1004,7 @@ int main(int argc, char** argv) {
   leveldb::g_env = leveldb::Env::Default();
 
   // Choose a location for the test database if none given with --db=<path>
-  if (FLAGS_db == NULL) {
+  if (FLAGS_db == nullptr) {
       leveldb::g_env->GetTestDirectory(&default_db_path);
       default_db_path += "/dbbench";
       FLAGS_db = default_db_path.c_str();
diff --git a/db/db_impl.cc b/db/db_impl.cc
index cd8792e..02a6872 100644
--- a/db/db_impl.cc
+++ b/db/db_impl.cc
@@ -77,8 +77,8 @@ struct DBImpl::CompactionState {
 
   explicit CompactionState(Compaction* c)
       : compaction(c),
-        outfile(NULL),
-        builder(NULL),
+        outfile(nullptr),
+        builder(nullptr),
         total_bytes(0) {
   }
 };
@@ -95,22 +95,22 @@ Options SanitizeOptions(const std::string& dbname,
                         const Options& src) {
   Options result = src;
   result.comparator = icmp;
-  result.filter_policy = (src.filter_policy != NULL) ? ipolicy : NULL;
+  result.filter_policy = (src.filter_policy != nullptr) ? ipolicy : nullptr;
   ClipToRange(&result.max_open_files,    64 + kNumNonTableCacheFiles, 50000);
   ClipToRange(&result.write_buffer_size, 64<<10,                      1<<30);
   ClipToRange(&result.max_file_size,     1<<20,                       1<<30);
   ClipToRange(&result.block_size,        1<<10,                       4<<20);
-  if (result.info_log == NULL) {
+  if (result.info_log == nullptr) {
     // Open a log file in the same directory as the db
     src.env->CreateDir(dbname);  // In case it does not exist
     src.env->RenameFile(InfoLogFileName(dbname), OldInfoLogFileName(dbname));
     Status s = src.env->NewLogger(InfoLogFileName(dbname), &result.info_log);
     if (!s.ok()) {
       // No place suitable for logging
-      result.info_log = NULL;
+      result.info_log = nullptr;
     }
   }
-  if (result.block_cache == NULL) {
+  if (result.block_cache == nullptr) {
     result.block_cache = NewLRUCache(8 << 20);
   }
   return result;
@@ -131,39 +131,39 @@ DBImpl::DBImpl(const Options& raw_options, const std::string& dbname)
       owns_cache_(options_.block_cache != raw_options.block_cache),
       dbname_(dbname),
       table_cache_(new TableCache(dbname_, options_, TableCacheSize(options_))),
-      db_lock_(NULL),
-      shutting_down_(NULL),
+      db_lock_(nullptr),
+      shutting_down_(nullptr),
       background_work_finished_signal_(&mutex_),
-      mem_(NULL),
-      imm_(NULL),
-      logfile_(NULL),
+      mem_(nullptr),
+      imm_(nullptr),
+      logfile_(nullptr),
       logfile_number_(0),
-      log_(NULL),
+      log_(nullptr),
       seed_(0),
       tmp_batch_(new WriteBatch),
       background_compaction_scheduled_(false),
-      manual_compaction_(NULL),
+      manual_compaction_(nullptr),
       versions_(new VersionSet(dbname_, &options_, table_cache_,
                                &internal_comparator_)) {
-  has_imm_.Release_Store(NULL);
+  has_imm_.Release_Store(nullptr);
 }
 
 DBImpl::~DBImpl() {
   // Wait for background work to finish
   mutex_.Lock();
-  shutting_down_.Release_Store(this);  // Any non-NULL value is ok
+  shutting_down_.Release_Store(this);  // Any non-null value is ok
   while (background_compaction_scheduled_) {
     background_work_finished_signal_.Wait();
   }
   mutex_.Unlock();
 
-  if (db_lock_ != NULL) {
+  if (db_lock_ != nullptr) {
     env_->UnlockFile(db_lock_);
   }
 
   delete versions_;
-  if (mem_ != NULL) mem_->Unref();
-  if (imm_ != NULL) imm_->Unref();
+  if (mem_ != nullptr) mem_->Unref();
+  if (imm_ != nullptr) imm_->Unref();
   delete tmp_batch_;
   delete log_;
   delete logfile_;
@@ -283,7 +283,7 @@ Status DBImpl::Recover(VersionEdit* edit, bool *save_manifest) {
   // committed only when the descriptor is created, and this directory
   // may already exist from a previous failed creation attempt.
   env_->CreateDir(dbname_);
-  assert(db_lock_ == NULL);
+  assert(db_lock_ == nullptr);
   Status s = env_->LockFile(LockFileName(dbname_), &db_lock_);
   if (!s.ok()) {
     return s;
@@ -374,12 +374,12 @@ Status DBImpl::RecoverLogFile(uint64_t log_number, bool last_log,
     Env* env;
     Logger* info_log;
     const char* fname;
-    Status* status;  // NULL if options_.paranoid_checks==false
+    Status* status;  // null if options_.paranoid_checks==false
     virtual void Corruption(size_t bytes, const Status& s) {
       Log(info_log, "%s%s: dropping %d bytes; %s",
-          (this->status == NULL ? "(ignoring error) " : ""),
+          (this->status == nullptr ? "(ignoring error) " : ""),
           fname, static_cast<int>(bytes), s.ToString().c_str());
-      if (this->status != NULL && this->status->ok()) *this->status = s;
+      if (this->status != nullptr && this->status->ok()) *this->status = s;
     }
   };
 
@@ -399,7 +399,7 @@ Status DBImpl::RecoverLogFile(uint64_t log_number, bool last_log,
   reporter.env = env_;
   reporter.info_log = options_.info_log;
   reporter.fname = fname.c_str();
-  reporter.status = (options_.paranoid_checks ? &status : NULL);
+  reporter.status = (options_.paranoid_checks ? &status : nullptr);
   // We intentionally make log::Reader do checksumming even if
   // paranoid_checks==false so that corruptions cause entire commits
   // to be skipped instead of propagating bad information (like overly
@@ -414,7 +414,7 @@ Status DBImpl::RecoverLogFile(uint64_t log_number, bool last_log,
   Slice record;
   WriteBatch batch;
   int compactions = 0;
-  MemTable* mem = NULL;
+  MemTable* mem = nullptr;
   while (reader.ReadRecord(&record, &scratch) &&
          status.ok()) {
     if (record.size() < 12) {
@@ -424,7 +424,7 @@ Status DBImpl::RecoverLogFile(uint64_t log_number, bool last_log,
     }
     WriteBatchInternal::SetContents(&batch, record);
 
-    if (mem == NULL) {
+    if (mem == nullptr) {
       mem = new MemTable(internal_comparator_);
       mem->Ref();
     }
@@ -443,9 +443,9 @@ Status DBImpl::RecoverLogFile(uint64_t log_number, bool last_log,
     if (mem->ApproximateMemoryUsage() > options_.write_buffer_size) {
       compactions++;
       *save_manifest = true;
-      status = WriteLevel0Table(mem, edit, NULL);
+      status = WriteLevel0Table(mem, edit, nullptr);
       mem->Unref();
-      mem = NULL;
+      mem = nullptr;
       if (!status.ok()) {
         // Reflect errors immediately so that conditions like full
         // file-systems cause the DB::Open() to fail.
@@ -458,31 +458,31 @@ Status DBImpl::RecoverLogFile(uint64_t log_number, bool last_log,
 
   // See if we should keep reusing the last log file.
   if (status.ok() && options_.reuse_logs && last_log && compactions == 0) {
-    assert(logfile_ == NULL);
-    assert(log_ == NULL);
-    assert(mem_ == NULL);
+    assert(logfile_ == nullptr);
+    assert(log_ == nullptr);
+    assert(mem_ == nullptr);
     uint64_t lfile_size;
     if (env_->GetFileSize(fname, &lfile_size).ok() &&
         env_->NewAppendableFile(fname, &logfile_).ok()) {
       Log(options_.info_log, "Reusing old log %s \n", fname.c_str());
       log_ = new log::Writer(logfile_, lfile_size);
       logfile_number_ = log_number;
-      if (mem != NULL) {
+      if (mem != nullptr) {
         mem_ = mem;
-        mem = NULL;
+        mem = nullptr;
       } else {
-        // mem can be NULL if lognum exists but was empty.
+        // mem can be nullptr if lognum exists but was empty.
         mem_ = new MemTable(internal_comparator_);
         mem_->Ref();
       }
     }
   }
 
-  if (mem != NULL) {
+  if (mem != nullptr) {
     // mem did not get reused; compact it.
     if (status.ok()) {
       *save_manifest = true;
-      status = WriteLevel0Table(mem, edit, NULL);
+      status = WriteLevel0Table(mem, edit, nullptr);
     }
     mem->Unref();
   }
@@ -522,7 +522,7 @@ Status DBImpl::WriteLevel0Table(MemTable* mem, VersionEdit* edit,
   if (s.ok() && meta.file_size > 0) {
     const Slice min_user_key = meta.smallest.user_key();
     const Slice max_user_key = meta.largest.user_key();
-    if (base != NULL) {
+    if (base != nullptr) {
       level = base->PickLevelForMemTableOutput(min_user_key, max_user_key);
     }
     edit->AddFile(level, meta.number, meta.file_size,
@@ -538,7 +538,7 @@ Status DBImpl::WriteLevel0Table(MemTable* mem, VersionEdit* edit,
 
 void DBImpl::CompactMemTable() {
   mutex_.AssertHeld();
-  assert(imm_ != NULL);
+  assert(imm_ != nullptr);
 
   // Save the contents of the memtable as a new Table
   VersionEdit edit;
@@ -561,8 +561,8 @@ void DBImpl::CompactMemTable() {
   if (s.ok()) {
     // Commit to the new state
     imm_->Unref();
-    imm_ = NULL;
-    has_imm_.Release_Store(NULL);
+    imm_ = nullptr;
+    has_imm_.Release_Store(nullptr);
     DeleteObsoleteFiles();
   } else {
     RecordBackgroundError(s);
@@ -596,14 +596,14 @@ void DBImpl::TEST_CompactRange(int level, const Slice* begin,
   ManualCompaction manual;
   manual.level = level;
   manual.done = false;
-  if (begin == NULL) {
-    manual.begin = NULL;
+  if (begin == nullptr) {
+    manual.begin = nullptr;
   } else {
     begin_storage = InternalKey(*begin, kMaxSequenceNumber, kValueTypeForSeek);
     manual.begin = &begin_storage;
   }
-  if (end == NULL) {
-    manual.end = NULL;
+  if (end == nullptr) {
+    manual.end = nullptr;
   } else {
     end_storage = InternalKey(*end, 0, static_cast<ValueType>(0));
     manual.end = &end_storage;
@@ -611,7 +611,7 @@ void DBImpl::TEST_CompactRange(int level, const Slice* begin,
 
   MutexLock l(&mutex_);
   while (!manual.done && !shutting_down_.Acquire_Load() && bg_error_.ok()) {
-    if (manual_compaction_ == NULL) {  // Idle
+    if (manual_compaction_ == nullptr) {  // Idle
       manual_compaction_ = &manual;
       MaybeScheduleCompaction();
     } else {  // Running either my compaction or another compaction.
@@ -620,20 +620,20 @@ void DBImpl::TEST_CompactRange(int level, const Slice* begin,
   }
   if (manual_compaction_ == &manual) {
     // Cancel my manual compaction since we aborted early for some reason.
-    manual_compaction_ = NULL;
+    manual_compaction_ = nullptr;
   }
 }
 
 Status DBImpl::TEST_CompactMemTable() {
-  // NULL batch means just wait for earlier writes to be done
-  Status s = Write(WriteOptions(), NULL);
+  // nullptr batch means just wait for earlier writes to be done
+  Status s = Write(WriteOptions(), nullptr);
   if (s.ok()) {
     // Wait until the compaction completes
     MutexLock l(&mutex_);
-    while (imm_ != NULL && bg_error_.ok()) {
+    while (imm_ != nullptr && bg_error_.ok()) {
       background_work_finished_signal_.Wait();
     }
-    if (imm_ != NULL) {
+    if (imm_ != nullptr) {
       s = bg_error_;
     }
   }
@@ -656,8 +656,8 @@ void DBImpl::MaybeScheduleCompaction() {
     // DB is being deleted; no more background compactions
   } else if (!bg_error_.ok()) {
     // Already got an error; no more changes
-  } else if (imm_ == NULL &&
-             manual_compaction_ == NULL &&
+  } else if (imm_ == nullptr &&
+             manual_compaction_ == nullptr &&
              !versions_->NeedsCompaction()) {
     // No work to be done
   } else {
@@ -692,19 +692,19 @@ void DBImpl::BackgroundCall() {
 void DBImpl::BackgroundCompaction() {
   mutex_.AssertHeld();
 
-  if (imm_ != NULL) {
+  if (imm_ != nullptr) {
     CompactMemTable();
     return;
   }
 
   Compaction* c;
-  bool is_manual = (manual_compaction_ != NULL);
+  bool is_manual = (manual_compaction_ != nullptr);
   InternalKey manual_end;
   if (is_manual) {
     ManualCompaction* m = manual_compaction_;
     c = versions_->CompactRange(m->level, m->begin, m->end);
-    m->done = (c == NULL);
-    if (c != NULL) {
+    m->done = (c == nullptr);
+    if (c != nullptr) {
       manual_end = c->input(0, c->num_input_files(0) - 1)->largest;
     }
     Log(options_.info_log,
@@ -718,7 +718,7 @@ void DBImpl::BackgroundCompaction() {
   }
 
   Status status;
-  if (c == NULL) {
+  if (c == nullptr) {
     // Nothing to do
   } else if (!is_manual && c->IsTrivialMove()) {
     // Move file to next level
@@ -770,18 +770,18 @@ void DBImpl::BackgroundCompaction() {
       m->tmp_storage = manual_end;
       m->begin = &m->tmp_storage;
     }
-    manual_compaction_ = NULL;
+    manual_compaction_ = nullptr;
   }
 }
 
 void DBImpl::CleanupCompaction(CompactionState* compact) {
   mutex_.AssertHeld();
-  if (compact->builder != NULL) {
+  if (compact->builder != nullptr) {
     // May happen if we get a shutdown call in the middle of compaction
     compact->builder->Abandon();
     delete compact->builder;
   } else {
-    assert(compact->outfile == NULL);
+    assert(compact->outfile == nullptr);
   }
   delete compact->outfile;
   for (size_t i = 0; i < compact->outputs.size(); i++) {
@@ -792,8 +792,8 @@ void DBImpl::CleanupCompaction(CompactionState* compact) {
 }
 
 Status DBImpl::OpenCompactionOutputFile(CompactionState* compact) {
-  assert(compact != NULL);
-  assert(compact->builder == NULL);
+  assert(compact != nullptr);
+  assert(compact->builder == nullptr);
   uint64_t file_number;
   {
     mutex_.Lock();
@@ -818,9 +818,9 @@ Status DBImpl::OpenCompactionOutputFile(CompactionState* compact) {
 
 Status DBImpl::FinishCompactionOutputFile(CompactionState* compact,
                                           Iterator* input) {
-  assert(compact != NULL);
-  assert(compact->outfile != NULL);
-  assert(compact->builder != NULL);
+  assert(compact != nullptr);
+  assert(compact->outfile != nullptr);
+  assert(compact->builder != nullptr);
 
   const uint64_t output_number = compact->current_output()->number;
   assert(output_number != 0);
@@ -837,7 +837,7 @@ Status DBImpl::FinishCompactionOutputFile(CompactionState* compact,
   compact->current_output()->file_size = current_bytes;
   compact->total_bytes += current_bytes;
   delete compact->builder;
-  compact->builder = NULL;
+  compact->builder = nullptr;
 
   // Finish and check for file errors
   if (s.ok()) {
@@ -847,7 +847,7 @@ Status DBImpl::FinishCompactionOutputFile(CompactionState* compact,
     s = compact->outfile->Close();
   }
   delete compact->outfile;
-  compact->outfile = NULL;
+  compact->outfile = nullptr;
 
   if (s.ok() && current_entries > 0) {
     // Verify that the table is usable
@@ -901,8 +901,8 @@ Status DBImpl::DoCompactionWork(CompactionState* compact) {
       compact->compaction->level() + 1);
 
   assert(versions_->NumLevelFiles(compact->compaction->level()) > 0);
-  assert(compact->builder == NULL);
-  assert(compact->outfile == NULL);
+  assert(compact->builder == nullptr);
+  assert(compact->outfile == nullptr);
   if (snapshots_.empty()) {
     compact->smallest_snapshot = versions_->LastSequence();
   } else {
@@ -921,10 +921,10 @@ Status DBImpl::DoCompactionWork(CompactionState* compact) {
   SequenceNumber last_sequence_for_key = kMaxSequenceNumber;
   for (; input->Valid() && !shutting_down_.Acquire_Load(); ) {
     // Prioritize immutable compaction work
-    if (has_imm_.NoBarrier_Load() != NULL) {
+    if (has_imm_.NoBarrier_Load() != nullptr) {
       const uint64_t imm_start = env_->NowMicros();
       mutex_.Lock();
-      if (imm_ != NULL) {
+      if (imm_ != nullptr) {
         CompactMemTable();
         // Wake up MakeRoomForWrite() if necessary.
         background_work_finished_signal_.SignalAll();
@@ -935,7 +935,7 @@ Status DBImpl::DoCompactionWork(CompactionState* compact) {
 
     Slice key = input->key();
     if (compact->compaction->ShouldStopBefore(key) &&
-        compact->builder != NULL) {
+        compact->builder != nullptr) {
       status = FinishCompactionOutputFile(compact, input);
       if (!status.ok()) {
         break;
@@ -989,7 +989,7 @@ Status DBImpl::DoCompactionWork(CompactionState* compact) {
 
     if (!drop) {
       // Open output file if necessary
-      if (compact->builder == NULL) {
+      if (compact->builder == nullptr) {
         status = OpenCompactionOutputFile(compact);
         if (!status.ok()) {
           break;
@@ -1017,14 +1017,14 @@ Status DBImpl::DoCompactionWork(CompactionState* compact) {
   if (status.ok() && shutting_down_.Acquire_Load()) {
     status = Status::IOError("Deleting DB during compaction");
   }
-  if (status.ok() && compact->builder != NULL) {
+  if (status.ok() && compact->builder != nullptr) {
     status = FinishCompactionOutputFile(compact, input);
   }
   if (status.ok()) {
     status = input->status();
   }
   delete input;
-  input = NULL;
+  input = nullptr;
 
   CompactionStats stats;
   stats.micros = env_->NowMicros() - start_micros - imm_micros;
@@ -1068,7 +1068,7 @@ static void CleanupIteratorState(void* arg1, void* arg2) {
   IterState* state = reinterpret_cast<IterState*>(arg1);
   state->mu->Lock();
   state->mem->Unref();
-  if (state->imm != NULL) state->imm->Unref();
+  if (state->imm != nullptr) state->imm->Unref();
   state->version->Unref();
   state->mu->Unlock();
   delete state;
@@ -1086,7 +1086,7 @@ Iterator* DBImpl::NewInternalIterator(const ReadOptions& options,
   std::vector<Iterator*> list;
   list.push_back(mem_->NewIterator());
   mem_->Ref();
-  if (imm_ != NULL) {
+  if (imm_ != nullptr) {
     list.push_back(imm_->NewIterator());
     imm_->Ref();
   }
@@ -1096,7 +1096,7 @@ Iterator* DBImpl::NewInternalIterator(const ReadOptions& options,
   versions_->current()->Ref();
 
   IterState* cleanup = new IterState(&mutex_, mem_, imm_, versions_->current());
-  internal_iter->RegisterCleanup(CleanupIteratorState, cleanup, NULL);
+  internal_iter->RegisterCleanup(CleanupIteratorState, cleanup, nullptr);
 
   *seed = ++seed_;
   mutex_.Unlock();
@@ -1120,7 +1120,7 @@ Status DBImpl::Get(const ReadOptions& options,
   Status s;
   MutexLock l(&mutex_);
   SequenceNumber snapshot;
-  if (options.snapshot != NULL) {
+  if (options.snapshot != nullptr) {
     snapshot = reinterpret_cast<const SnapshotImpl*>(options.snapshot)->number_;
   } else {
     snapshot = versions_->LastSequence();
@@ -1130,7 +1130,7 @@ Status DBImpl::Get(const ReadOptions& options,
   MemTable* imm = imm_;
   Version* current = versions_->current();
   mem->Ref();
-  if (imm != NULL) imm->Ref();
+  if (imm != nullptr) imm->Ref();
   current->Ref();
 
   bool have_stat_update = false;
@@ -1143,7 +1143,7 @@ Status DBImpl::Get(const ReadOptions& options,
     LookupKey lkey(key, snapshot);
     if (mem->Get(lkey, value, &s)) {
       // Done
-    } else if (imm != NULL && imm->Get(lkey, value, &s)) {
+    } else if (imm != nullptr && imm->Get(lkey, value, &s)) {
       // Done
     } else {
       s = current->Get(options, lkey, value, &stats);
@@ -1156,7 +1156,7 @@ Status DBImpl::Get(const ReadOptions& options,
     MaybeScheduleCompaction();
   }
   mem->Unref();
-  if (imm != NULL) imm->Unref();
+  if (imm != nullptr) imm->Unref();
   current->Unref();
   return s;
 }
@@ -1167,7 +1167,7 @@ Iterator* DBImpl::NewIterator(const ReadOptions& options) {
   Iterator* iter = NewInternalIterator(options, &latest_snapshot, &seed);
   return NewDBIterator(
       this, user_comparator(), iter,
-      (options.snapshot != NULL
+      (options.snapshot != nullptr
        ? reinterpret_cast<const SnapshotImpl*>(options.snapshot)->number_
        : latest_snapshot),
       seed);
@@ -1215,10 +1215,10 @@ Status DBImpl::Write(const WriteOptions& options, WriteBatch* my_batch) {
   }
 
   // May temporarily unlock and wait.
-  Status status = MakeRoomForWrite(my_batch == NULL);
+  Status status = MakeRoomForWrite(my_batch == nullptr);
   uint64_t last_sequence = versions_->LastSequence();
   Writer* last_writer = &w;
-  if (status.ok() && my_batch != NULL) {  // NULL batch is for compactions
+  if (status.ok() && my_batch != nullptr) {  // nullptr batch is for compactions
     WriteBatch* updates = BuildBatchGroup(&last_writer);
     WriteBatchInternal::SetSequence(updates, last_sequence + 1);
     last_sequence += WriteBatchInternal::Count(updates);
@@ -1273,13 +1273,13 @@ Status DBImpl::Write(const WriteOptions& options, WriteBatch* my_batch) {
 }
 
 // REQUIRES: Writer list must be non-empty
-// REQUIRES: First writer must have a non-NULL batch
+// REQUIRES: First writer must have a non-null batch
 WriteBatch* DBImpl::BuildBatchGroup(Writer** last_writer) {
   mutex_.AssertHeld();
   assert(!writers_.empty());
   Writer* first = writers_.front();
   WriteBatch* result = first->batch;
-  assert(result != NULL);
+  assert(result != nullptr);
 
   size_t size = WriteBatchInternal::ByteSize(first->batch);
 
@@ -1301,7 +1301,7 @@ WriteBatch* DBImpl::BuildBatchGroup(Writer** last_writer) {
       break;
     }
 
-    if (w->batch != NULL) {
+    if (w->batch != nullptr) {
       size += WriteBatchInternal::ByteSize(w->batch);
       if (size > max_size) {
         // Do not make batch too big
@@ -1351,7 +1351,7 @@ Status DBImpl::MakeRoomForWrite(bool force) {
                (mem_->ApproximateMemoryUsage() <= options_.write_buffer_size)) {
       // There is room in current memtable
       break;
-    } else if (imm_ != NULL) {
+    } else if (imm_ != nullptr) {
       // We have filled up the current memtable, but the previous
       // one is still being compacted, so we wait.
       Log(options_.info_log, "Current memtable full; waiting...\n");
@@ -1364,7 +1364,7 @@ Status DBImpl::MakeRoomForWrite(bool force) {
       // Attempt to switch to a new memtable and trigger compaction of old
       assert(versions_->PrevLogNumber() == 0);
       uint64_t new_log_number = versions_->NewFileNumber();
-      WritableFile* lfile = NULL;
+      WritableFile* lfile = nullptr;
       s = env_->NewWritableFile(LogFileName(dbname_, new_log_number), &lfile);
       if (!s.ok()) {
         // Avoid chewing through file number space in a tight loop.
@@ -1498,7 +1498,7 @@ DB::~DB() { }
 
 Status DB::Open(const Options& options, const std::string& dbname,
                 DB** dbptr) {
-  *dbptr = NULL;
+  *dbptr = nullptr;
 
   DBImpl* impl = new DBImpl(options, dbname);
   impl->mutex_.Lock();
@@ -1506,7 +1506,7 @@ Status DB::Open(const Options& options, const std::string& dbname,
   // Recover handles create_if_missing, error_if_exists
   bool save_manifest = false;
   Status s = impl->Recover(&edit, &save_manifest);
-  if (s.ok() && impl->mem_ == NULL) {
+  if (s.ok() && impl->mem_ == nullptr) {
     // Create new log and a corresponding memtable.
     uint64_t new_log_number = impl->versions_->NewFileNumber();
     WritableFile* lfile;
@@ -1532,7 +1532,7 @@ Status DB::Open(const Options& options, const std::string& dbname,
   }
   impl->mutex_.Unlock();
   if (s.ok()) {
-    assert(impl->mem_ != NULL);
+    assert(impl->mem_ != nullptr);
     *dbptr = impl;
   } else {
     delete impl;
diff --git a/db/db_impl.h b/db/db_impl.h
index 6344112..00e800a 100644
--- a/db/db_impl.h
+++ b/db/db_impl.h
@@ -131,7 +131,7 @@ class DBImpl : public DB {
   // table_cache_ provides its own synchronization
   TableCache* const table_cache_;
 
-  // Lock over the persistent DB state.  Non-NULL iff successfully acquired.
+  // Lock over the persistent DB state.  Non-null iff successfully acquired.
   FileLock* db_lock_;
 
   // State below is protected by mutex_
@@ -140,7 +140,7 @@ class DBImpl : public DB {
   port::CondVar background_work_finished_signal_ GUARDED_BY(mutex_);
   MemTable* mem_;
   MemTable* imm_ GUARDED_BY(mutex_);  // Memtable being compacted
-  port::AtomicPointer has_imm_;       // So bg thread can detect non-NULL imm_
+  port::AtomicPointer has_imm_;       // So bg thread can detect non-null imm_
   WritableFile* logfile_;
   uint64_t logfile_number_ GUARDED_BY(mutex_);
   log::Writer* log_;
@@ -163,8 +163,8 @@ class DBImpl : public DB {
   struct ManualCompaction {
     int level;
     bool done;
-    const InternalKey* begin;   // NULL means beginning of key range
-    const InternalKey* end;     // NULL means end of key range
+    const InternalKey* begin;   // null means beginning of key range
+    const InternalKey* end;     // null means end of key range
     InternalKey tmp_storage;    // Used to keep track of compaction progress
   };
   ManualCompaction* manual_compaction_ GUARDED_BY(mutex_);
diff --git a/db/db_test.cc b/db/db_test.cc
index b1d2cd8..47e3287 100644
--- a/db/db_test.cc
+++ b/db/db_test.cc
@@ -96,35 +96,35 @@ class TestEnv : public EnvWrapper {
 // Special Env used to delay background operations
 class SpecialEnv : public EnvWrapper {
  public:
-  // sstable/log Sync() calls are blocked while this pointer is non-NULL.
+  // sstable/log Sync() calls are blocked while this pointer is non-null.
   port::AtomicPointer delay_data_sync_;
 
   // sstable/log Sync() calls return an error.
   port::AtomicPointer data_sync_error_;
 
-  // Simulate no-space errors while this pointer is non-NULL.
+  // Simulate no-space errors while this pointer is non-null.
   port::AtomicPointer no_space_;
 
-  // Simulate non-writable file system while this pointer is non-NULL
+  // Simulate non-writable file system while this pointer is non-null.
   port::AtomicPointer non_writable_;
 
-  // Force sync of manifest files to fail while this pointer is non-NULL
+  // Force sync of manifest files to fail while this pointer is non-null.
   port::AtomicPointer manifest_sync_error_;
 
-  // Force write to manifest files to fail while this pointer is non-NULL
+  // Force write to manifest files to fail while this pointer is non-null.
   port::AtomicPointer manifest_write_error_;
 
   bool count_random_reads_;
   AtomicCounter random_read_counter_;
 
   explicit SpecialEnv(Env* base) : EnvWrapper(base) {
-    delay_data_sync_.Release_Store(NULL);
-    data_sync_error_.Release_Store(NULL);
-    no_space_.Release_Store(NULL);
-    non_writable_.Release_Store(NULL);
+    delay_data_sync_.Release_Store(nullptr);
+    data_sync_error_.Release_Store(nullptr);
+    no_space_.Release_Store(nullptr);
+    non_writable_.Release_Store(nullptr);
     count_random_reads_ = false;
-    manifest_sync_error_.Release_Store(NULL);
-    manifest_write_error_.Release_Store(NULL);
+    manifest_sync_error_.Release_Store(nullptr);
+    manifest_write_error_.Release_Store(nullptr);
   }
 
   Status NewWritableFile(const std::string& f, WritableFile** r) {
@@ -140,7 +140,7 @@ class SpecialEnv : public EnvWrapper {
       }
       ~DataFile() { delete base_; }
       Status Append(const Slice& data) {
-        if (env_->no_space_.Acquire_Load() != NULL) {
+        if (env_->no_space_.Acquire_Load() != nullptr) {
           // Drop writes on the floor
           return Status::OK();
         } else {
@@ -150,10 +150,10 @@ class SpecialEnv : public EnvWrapper {
       Status Close() { return base_->Close(); }
       Status Flush() { return base_->Flush(); }
       Status Sync() {
-        if (env_->data_sync_error_.Acquire_Load() != NULL) {
+        if (env_->data_sync_error_.Acquire_Load() != nullptr) {
           return Status::IOError("simulated data sync error");
         }
-        while (env_->delay_data_sync_.Acquire_Load() != NULL) {
+        while (env_->delay_data_sync_.Acquire_Load() != nullptr) {
           DelayMilliseconds(100);
         }
         return base_->Sync();
@@ -167,7 +167,7 @@ class SpecialEnv : public EnvWrapper {
       ManifestFile(SpecialEnv* env, WritableFile* b) : env_(env), base_(b) { }
       ~ManifestFile() { delete base_; }
       Status Append(const Slice& data) {
-        if (env_->manifest_write_error_.Acquire_Load() != NULL) {
+        if (env_->manifest_write_error_.Acquire_Load() != nullptr) {
           return Status::IOError("simulated writer error");
         } else {
           return base_->Append(data);
@@ -176,7 +176,7 @@ class SpecialEnv : public EnvWrapper {
       Status Close() { return base_->Close(); }
       Status Flush() { return base_->Flush(); }
       Status Sync() {
-        if (env_->manifest_sync_error_.Acquire_Load() != NULL) {
+        if (env_->manifest_sync_error_.Acquire_Load() != nullptr) {
           return Status::IOError("simulated sync error");
         } else {
           return base_->Sync();
@@ -184,16 +184,16 @@ class SpecialEnv : public EnvWrapper {
       }
     };
 
-    if (non_writable_.Acquire_Load() != NULL) {
+    if (non_writable_.Acquire_Load() != nullptr) {
       return Status::IOError("simulated write error");
     }
 
     Status s = target()->NewWritableFile(f, r);
     if (s.ok()) {
-      if (strstr(f.c_str(), ".ldb") != NULL ||
-          strstr(f.c_str(), ".log") != NULL) {
+      if (strstr(f.c_str(), ".ldb") != nullptr ||
+          strstr(f.c_str(), ".log") != nullptr) {
         *r = new DataFile(this, *r);
-      } else if (strstr(f.c_str(), "MANIFEST") != NULL) {
+      } else if (strstr(f.c_str(), "MANIFEST") != nullptr) {
         *r = new ManifestFile(this, *r);
       }
     }
@@ -251,7 +251,7 @@ class DBTest {
     filter_policy_ = NewBloomFilterPolicy(10);
     dbname_ = test::TmpDir() + "/db_test";
     DestroyDB(dbname_, Options());
-    db_ = NULL;
+    db_ = nullptr;
     Reopen();
   }
 
@@ -298,27 +298,27 @@ class DBTest {
     return reinterpret_cast<DBImpl*>(db_);
   }
 
-  void Reopen(Options* options = NULL) {
+  void Reopen(Options* options = nullptr) {
     ASSERT_OK(TryReopen(options));
   }
 
   void Close() {
     delete db_;
-    db_ = NULL;
+    db_ = nullptr;
   }
 
-  void DestroyAndReopen(Options* options = NULL) {
+  void DestroyAndReopen(Options* options = nullptr) {
     delete db_;
-    db_ = NULL;
+    db_ = nullptr;
     DestroyDB(dbname_, Options());
     ASSERT_OK(TryReopen(options));
   }
 
   Status TryReopen(Options* options) {
     delete db_;
-    db_ = NULL;
+    db_ = nullptr;
     Options opts;
-    if (options != NULL) {
+    if (options != nullptr) {
       opts = *options;
     } else {
       opts = CurrentOptions();
@@ -337,7 +337,7 @@ class DBTest {
     return db_->Delete(WriteOptions(), k);
   }
 
-  std::string Get(const std::string& k, const Snapshot* snapshot = NULL) {
+  std::string Get(const std::string& k, const Snapshot* snapshot = nullptr) {
     ReadOptions options;
     options.snapshot = snapshot;
     std::string result;
@@ -549,7 +549,7 @@ class DBTest {
 
 TEST(DBTest, Empty) {
   do {
-    ASSERT_TRUE(db_ != NULL);
+    ASSERT_TRUE(db_ != nullptr);
     ASSERT_EQ("NOT_FOUND", Get("foo"));
   } while (ChangeOptions());
 }
@@ -590,7 +590,7 @@ TEST(DBTest, GetFromImmutableLayer) {
     Put("k1", std::string(100000, 'x'));             // Fill memtable
     Put("k2", std::string(100000, 'y'));             // Trigger compaction
     ASSERT_EQ("v1", Get("foo"));
-    env_->delay_data_sync_.Release_Store(NULL);      // Release sync calls
+    env_->delay_data_sync_.Release_Store(nullptr);   // Release sync calls
   } while (ChangeOptions());
 }
 
@@ -695,7 +695,7 @@ TEST(DBTest, GetEncountersEmptyLevel) {
     }
 
     // Step 2: clear level 1 if necessary.
-    dbfull()->TEST_CompactRange(1, NULL, NULL);
+    dbfull()->TEST_CompactRange(1, nullptr, nullptr);
     ASSERT_EQ(NumTableFilesAtLevel(0), 1);
     ASSERT_EQ(NumTableFilesAtLevel(1), 0);
     ASSERT_EQ(NumTableFilesAtLevel(2), 1);
@@ -1032,7 +1032,7 @@ TEST(DBTest, CompactionsGenerateMultipleFiles) {
 
   // Reopening moves updates to level-0
   Reopen(&options);
-  dbfull()->TEST_CompactRange(0, NULL, NULL);
+  dbfull()->TEST_CompactRange(0, nullptr, nullptr);
 
   ASSERT_EQ(NumTableFilesAtLevel(0), 0);
   ASSERT_GT(NumTableFilesAtLevel(1), 1);
@@ -1083,7 +1083,7 @@ TEST(DBTest, SparseMerge) {
   }
   Put("C", "vc");
   dbfull()->TEST_CompactMemTable();
-  dbfull()->TEST_CompactRange(0, NULL, NULL);
+  dbfull()->TEST_CompactRange(0, nullptr, nullptr);
 
   // Make sparse update
   Put("A",    "va2");
@@ -1094,9 +1094,9 @@ TEST(DBTest, SparseMerge) {
   // Compactions should not cause us to create a situation where
   // a file overlaps too much data at the next level.
   ASSERT_LE(dbfull()->TEST_MaxNextLevelOverlappingBytes(), 20*1048576);
-  dbfull()->TEST_CompactRange(0, NULL, NULL);
+  dbfull()->TEST_CompactRange(0, nullptr, nullptr);
   ASSERT_LE(dbfull()->TEST_MaxNextLevelOverlappingBytes(), 20*1048576);
-  dbfull()->TEST_CompactRange(1, NULL, NULL);
+  dbfull()->TEST_CompactRange(1, nullptr, nullptr);
   ASSERT_LE(dbfull()->TEST_MaxNextLevelOverlappingBytes(), 20*1048576);
 }
 
@@ -1207,7 +1207,7 @@ TEST(DBTest, ApproximateSizes_MixOfSmallAndLarge) {
 
       ASSERT_TRUE(Between(Size(Key(3), Key(5)), 110000, 111000));
 
-      dbfull()->TEST_CompactRange(0, NULL, NULL);
+      dbfull()->TEST_CompactRange(0, nullptr, nullptr);
     }
   } while (ChangeOptions());
 }
@@ -1283,11 +1283,11 @@ TEST(DBTest, HiddenValuesAreRemoved) {
     db_->ReleaseSnapshot(snapshot);
     ASSERT_EQ(AllEntriesFor("foo"), "[ tiny, " + big + " ]");
     Slice x("x");
-    dbfull()->TEST_CompactRange(0, NULL, &x);
+    dbfull()->TEST_CompactRange(0, nullptr, &x);
     ASSERT_EQ(AllEntriesFor("foo"), "[ tiny ]");
     ASSERT_EQ(NumTableFilesAtLevel(0), 0);
     ASSERT_GE(NumTableFilesAtLevel(1), 1);
-    dbfull()->TEST_CompactRange(1, NULL, &x);
+    dbfull()->TEST_CompactRange(1, nullptr, &x);
     ASSERT_EQ(AllEntriesFor("foo"), "[ tiny ]");
 
     ASSERT_TRUE(Between(Size("", "pastfoo"), 0, 1000));
@@ -1313,11 +1313,11 @@ TEST(DBTest, DeletionMarkers1) {
   ASSERT_OK(dbfull()->TEST_CompactMemTable());  // Moves to level last-2
   ASSERT_EQ(AllEntriesFor("foo"), "[ v2, DEL, v1 ]");
   Slice z("z");
-  dbfull()->TEST_CompactRange(last-2, NULL, &z);
+  dbfull()->TEST_CompactRange(last-2, nullptr, &z);
   // DEL eliminated, but v1 remains because we aren't compacting that level
   // (DEL can be eliminated because v2 hides v1).
   ASSERT_EQ(AllEntriesFor("foo"), "[ v2, v1 ]");
-  dbfull()->TEST_CompactRange(last-1, NULL, NULL);
+  dbfull()->TEST_CompactRange(last-1, nullptr, nullptr);
   // Merging last-1 w/ last, so we are the base level for "foo", so
   // DEL is removed.  (as is v1).
   ASSERT_EQ(AllEntriesFor("foo"), "[ v2 ]");
@@ -1340,10 +1340,10 @@ TEST(DBTest, DeletionMarkers2) {
   ASSERT_EQ(AllEntriesFor("foo"), "[ DEL, v1 ]");
   ASSERT_OK(dbfull()->TEST_CompactMemTable());  // Moves to level last-2
   ASSERT_EQ(AllEntriesFor("foo"), "[ DEL, v1 ]");
-  dbfull()->TEST_CompactRange(last-2, NULL, NULL);
+  dbfull()->TEST_CompactRange(last-2, nullptr, nullptr);
   // DEL kept: "last" file overlaps
   ASSERT_EQ(AllEntriesFor("foo"), "[ DEL, v1 ]");
-  dbfull()->TEST_CompactRange(last-1, NULL, NULL);
+  dbfull()->TEST_CompactRange(last-1, nullptr, nullptr);
   // Merging last-1 w/ last, so we are the base level for "foo", so
   // DEL is removed.  (as is v1).
   ASSERT_EQ(AllEntriesFor("foo"), "[ ]");
@@ -1376,8 +1376,8 @@ TEST(DBTest, OverlapInLevel0) {
     ASSERT_EQ("2,1,1", FilesPerLevel());
 
     // Compact away the placeholder files we created initially
-    dbfull()->TEST_CompactRange(1, NULL, NULL);
-    dbfull()->TEST_CompactRange(2, NULL, NULL);
+    dbfull()->TEST_CompactRange(1, nullptr, nullptr);
+    dbfull()->TEST_CompactRange(2, nullptr, nullptr);
     ASSERT_EQ("2", FilesPerLevel());
 
     // Do a memtable compaction.  Before bug-fix, the compaction would
@@ -1437,7 +1437,7 @@ TEST(DBTest, Fflush_Issue474) {
   static const int kNum = 100000;
   Random rnd(test::RandomSeed());
   for (int i = 0; i < kNum; i++) {
-    fflush(NULL);
+    fflush(nullptr);
     ASSERT_OK(Put(RandomKey(&rnd), RandomString(&rnd, 100)));
   }
 }
@@ -1495,7 +1495,7 @@ TEST(DBTest, CustomComparator) {
   Options new_options = CurrentOptions();
   new_options.create_if_missing = true;
   new_options.comparator = &cmp;
-  new_options.filter_policy = NULL;     // Cannot use bloom filters
+  new_options.filter_policy = nullptr;     // Cannot use bloom filters
   new_options.write_buffer_size = 1000;  // Compact more often
   DestroyAndReopen(&new_options);
   ASSERT_OK(Put("[10]", "ten"));
@@ -1550,7 +1550,7 @@ TEST(DBTest, ManualCompaction) {
   // Compact all
   MakeTables(1, "a", "z");
   ASSERT_EQ("0,1,2", FilesPerLevel());
-  db_->CompactRange(NULL, NULL);
+  db_->CompactRange(nullptr, nullptr);
   ASSERT_EQ("0,0,1", FilesPerLevel());
 }
 
@@ -1559,38 +1559,38 @@ TEST(DBTest, DBOpen_Options) {
   DestroyDB(dbname, Options());
 
   // Does not exist, and create_if_missing == false: error
-  DB* db = NULL;
+  DB* db = nullptr;
   Options opts;
   opts.create_if_missing = false;
   Status s = DB::Open(opts, dbname, &db);
-  ASSERT_TRUE(strstr(s.ToString().c_str(), "does not exist") != NULL);
-  ASSERT_TRUE(db == NULL);
+  ASSERT_TRUE(strstr(s.ToString().c_str(), "does not exist") != nullptr);
+  ASSERT_TRUE(db == nullptr);
 
   // Does not exist, and create_if_missing == true: OK
   opts.create_if_missing = true;
   s = DB::Open(opts, dbname, &db);
   ASSERT_OK(s);
-  ASSERT_TRUE(db != NULL);
+  ASSERT_TRUE(db != nullptr);
 
   delete db;
-  db = NULL;
+  db = nullptr;
 
   // Does exist, and error_if_exists == true: error
   opts.create_if_missing = false;
   opts.error_if_exists = true;
   s = DB::Open(opts, dbname, &db);
-  ASSERT_TRUE(strstr(s.ToString().c_str(), "exists") != NULL);
-  ASSERT_TRUE(db == NULL);
+  ASSERT_TRUE(strstr(s.ToString().c_str(), "exists") != nullptr);
+  ASSERT_TRUE(db == nullptr);
 
   // Does exist, and error_if_exists == false: OK
   opts.create_if_missing = true;
   opts.error_if_exists = false;
   s = DB::Open(opts, dbname, &db);
   ASSERT_OK(s);
-  ASSERT_TRUE(db != NULL);
+  ASSERT_TRUE(db != nullptr);
 
   delete db;
-  db = NULL;
+  db = nullptr;
 }
 
 TEST(DBTest, DestroyEmptyDir) {
@@ -1628,9 +1628,9 @@ TEST(DBTest, DestroyOpenDB) {
 
   Options opts;
   opts.create_if_missing = true;
-  DB* db = NULL;
+  DB* db = nullptr;
   ASSERT_OK(DB::Open(opts, dbname, &db));
-  ASSERT_TRUE(db != NULL);
+  ASSERT_TRUE(db != nullptr);
 
   // Must fail to destroy an open db.
   ASSERT_TRUE(env_->FileExists(dbname));
@@ -1638,7 +1638,7 @@ TEST(DBTest, DestroyOpenDB) {
   ASSERT_TRUE(env_->FileExists(dbname));
 
   delete db;
-  db = NULL;
+  db = nullptr;
 
   // Should succeed destroying a closed db.
   ASSERT_OK(DestroyDB(dbname, Options()));
@@ -1646,7 +1646,7 @@ TEST(DBTest, DestroyOpenDB) {
 }
 
 TEST(DBTest, Locking) {
-  DB* db2 = NULL;
+  DB* db2 = nullptr;
   Status s = DB::Open(CurrentOptions(), dbname_, &db2);
   ASSERT_TRUE(!s.ok()) << "Locking did not prevent re-opening db";
 }
@@ -1664,10 +1664,10 @@ TEST(DBTest, NoSpace) {
   env_->no_space_.Release_Store(env_);   // Force out-of-space errors
   for (int i = 0; i < 10; i++) {
     for (int level = 0; level < config::kNumLevels-1; level++) {
-      dbfull()->TEST_CompactRange(level, NULL, NULL);
+      dbfull()->TEST_CompactRange(level, nullptr, nullptr);
     }
   }
-  env_->no_space_.Release_Store(NULL);
+  env_->no_space_.Release_Store(nullptr);
   ASSERT_LT(CountFiles(), num_files + 3);
 }
 
@@ -1688,7 +1688,7 @@ TEST(DBTest, NonWritableFileSystem) {
     }
   }
   ASSERT_GT(errors, 0);
-  env_->non_writable_.Release_Store(NULL);
+  env_->non_writable_.Release_Store(nullptr);
 }
 
 TEST(DBTest, WriteSyncError) {
@@ -1712,7 +1712,7 @@ TEST(DBTest, WriteSyncError) {
   ASSERT_EQ("NOT_FOUND", Get("k2"));
 
   // (d) make sync behave normally
-  env_->data_sync_error_.Release_Store(NULL);
+  env_->data_sync_error_.Release_Store(nullptr);
 
   // (e) Do a non-sync write; should fail
   w.sync = false;
@@ -1753,11 +1753,11 @@ TEST(DBTest, ManifestWriteError) {
 
     // Merging compaction (will fail)
     error_type->Release_Store(env_);
-    dbfull()->TEST_CompactRange(last, NULL, NULL);  // Should fail
+    dbfull()->TEST_CompactRange(last, nullptr, nullptr);  // Should fail
     ASSERT_EQ("bar", Get("foo"));
 
     // Recovery: should not lose data
-    error_type->Release_Store(NULL);
+    error_type->Release_Store(nullptr);
     Reopen(&options);
     ASSERT_EQ("bar", Get("foo"));
   }
@@ -1849,7 +1849,7 @@ TEST(DBTest, BloomFilter) {
   fprintf(stderr, "%d missing => %d reads\n", N, reads);
   ASSERT_LE(reads, 3*N/100);
 
-  env_->delay_data_sync_.Release_Store(NULL);
+  env_->delay_data_sync_.Release_Store(nullptr);
   Close();
   delete options.block_cache;
   delete options.filter_policy;
@@ -1883,7 +1883,7 @@ static void MTThreadBody(void* arg) {
   Random rnd(1000 + id);
   std::string value;
   char valbuf[1500];
-  while (t->state->stop.Acquire_Load() == NULL) {
+  while (t->state->stop.Acquire_Load() == nullptr) {
     t->state->counter[id].Release_Store(reinterpret_cast<void*>(counter));
 
     int key = rnd.Uniform(kNumKeys);
@@ -1946,7 +1946,7 @@ TEST(DBTest, MultiThreaded) {
     // Stop the threads and wait for them to finish
     mt.stop.Release_Store(&mt);
     for (int id = 0; id < kNumThreads; id++) {
-      while (mt.thread_done[id].Acquire_Load() == NULL) {
+      while (mt.thread_done[id].Acquire_Load() == nullptr) {
         DelayMilliseconds(100);
       }
     }
@@ -1978,7 +1978,7 @@ class ModelDB: public DB {
     return Status::NotFound(key);
   }
   virtual Iterator* NewIterator(const ReadOptions& options) {
-    if (options.snapshot == NULL) {
+    if (options.snapshot == nullptr) {
       KVMap* saved = new KVMap;
       *saved = map_;
       return new ModelIter(saved, true);
@@ -2112,8 +2112,8 @@ TEST(DBTest, Randomized) {
   do {
     ModelDB model(CurrentOptions());
     const int N = 10000;
-    const Snapshot* model_snap = NULL;
-    const Snapshot* db_snap = NULL;
+    const Snapshot* model_snap = nullptr;
+    const Snapshot* db_snap = nullptr;
     std::string k, v;
     for (int step = 0; step < N; step++) {
       if (step % 100 == 0) {
@@ -2158,23 +2158,23 @@ TEST(DBTest, Randomized) {
       }
 
       if ((step % 100) == 0) {
-        ASSERT_TRUE(CompareIterators(step, &model, db_, NULL, NULL));
+        ASSERT_TRUE(CompareIterators(step, &model, db_, nullptr, nullptr));
         ASSERT_TRUE(CompareIterators(step, &model, db_, model_snap, db_snap));
         // Save a snapshot from each DB this time that we'll use next
         // time we compare things, to make sure the current state is
         // preserved with the snapshot
-        if (model_snap != NULL) model.ReleaseSnapshot(model_snap);
-        if (db_snap != NULL) db_->ReleaseSnapshot(db_snap);
+        if (model_snap != nullptr) model.ReleaseSnapshot(model_snap);
+        if (db_snap != nullptr) db_->ReleaseSnapshot(db_snap);
 
         Reopen();
-        ASSERT_TRUE(CompareIterators(step, &model, db_, NULL, NULL));
+        ASSERT_TRUE(CompareIterators(step, &model, db_, nullptr, nullptr));
 
         model_snap = model.GetSnapshot();
         db_snap = db_->GetSnapshot();
       }
     }
-    if (model_snap != NULL) model.ReleaseSnapshot(model_snap);
-    if (db_snap != NULL) db_->ReleaseSnapshot(db_snap);
+    if (model_snap != nullptr) model.ReleaseSnapshot(model_snap);
+    if (db_snap != nullptr) db_->ReleaseSnapshot(db_snap);
   } while (ChangeOptions());
 }
 
@@ -2188,15 +2188,15 @@ void BM_LogAndApply(int iters, int num_base_files) {
   std::string dbname = test::TmpDir() + "/leveldb_test_benchmark";
   DestroyDB(dbname, Options());
 
-  DB* db = NULL;
+  DB* db = nullptr;
   Options opts;
   opts.create_if_missing = true;
   Status s = DB::Open(opts, dbname, &db);
   ASSERT_OK(s);
-  ASSERT_TRUE(db != NULL);
+  ASSERT_TRUE(db != nullptr);
 
   delete db;
-  db = NULL;
+  db = nullptr;
 
   Env* env = Env::Default();
 
@@ -2205,7 +2205,7 @@ void BM_LogAndApply(int iters, int num_base_files) {
 
   InternalKeyComparator cmp(BytewiseComparator());
   Options options;
-  VersionSet vset(dbname, &options, NULL, &cmp);
+  VersionSet vset(dbname, &options, nullptr, &cmp);
   bool save_manifest;
   ASSERT_OK(vset.Recover(&save_manifest));
   VersionEdit vbase;
diff --git a/db/dumpfile.cc b/db/dumpfile.cc
index 2f1b5d9..941988b 100644
--- a/db/dumpfile.cc
+++ b/db/dumpfile.cc
@@ -145,8 +145,8 @@ Status DumpDescriptor(Env* env, const std::string& fname, WritableFile* dst) {
 
 Status DumpTable(Env* env, const std::string& fname, WritableFile* dst) {
   uint64_t file_size;
-  RandomAccessFile* file = NULL;
-  Table* table = NULL;
+  RandomAccessFile* file = nullptr;
+  Table* table = nullptr;
   Status s = env->GetFileSize(fname, &file_size);
   if (s.ok()) {
     s = env->NewRandomAccessFile(fname, &file);
diff --git a/db/fault_injection_test.cc b/db/fault_injection_test.cc
index caead37..7894999 100644
--- a/db/fault_injection_test.cc
+++ b/db/fault_injection_test.cc
@@ -172,7 +172,7 @@ TestWritableFile::TestWritableFile(const FileState& state,
       target_(f),
       writable_file_opened_(true),
       env_(env) {
-  assert(f != NULL);
+  assert(f != nullptr);
 }
 
 TestWritableFile::~TestWritableFile() {
@@ -378,7 +378,7 @@ class FaultInjectionTest {
   FaultInjectionTest()
       : env_(new FaultInjectionTestEnv),
         tiny_cache_(NewLRUCache(100)),
-        db_(NULL) {
+        db_(nullptr) {
     dbname_ = test::TmpDir() + "/fault_test";
     DestroyDB(dbname_, Options());  // Destroy any db from earlier run
     options_.reuse_logs = true;
@@ -457,14 +457,14 @@ class FaultInjectionTest {
 
   Status OpenDB() {
     delete db_;
-    db_ = NULL;
+    db_ = nullptr;
     env_->ResetState();
     return DB::Open(options_, dbname_, &db_);
   }
 
   void CloseDB() {
     delete db_;
-    db_ = NULL;
+    db_ = nullptr;
   }
 
   void DeleteAllData() {
@@ -493,7 +493,7 @@ class FaultInjectionTest {
   void PartialCompactTestPreFault(int num_pre_sync, int num_post_sync) {
     DeleteAllData();
     Build(0, num_pre_sync);
-    db_->CompactRange(NULL, NULL);
+    db_->CompactRange(nullptr, nullptr);
     Build(num_pre_sync, num_post_sync);
   }
 
diff --git a/db/log_reader.cc b/db/log_reader.cc
index 48ae863..19c4df6 100644
--- a/db/log_reader.cc
+++ b/db/log_reader.cc
@@ -185,7 +185,7 @@ void Reader::ReportCorruption(uint64_t bytes, const char* reason) {
 }
 
 void Reader::ReportDrop(uint64_t bytes, const Status& reason) {
-  if (reporter_ != NULL &&
+  if (reporter_ != nullptr &&
       end_of_buffer_offset_ - buffer_.size() - bytes >= initial_offset_) {
     reporter_->Corruption(static_cast<size_t>(bytes), reason);
   }
diff --git a/db/log_reader.h b/db/log_reader.h
index 8389d61..7dcce8e 100644
--- a/db/log_reader.h
+++ b/db/log_reader.h
@@ -32,7 +32,7 @@ class Reader {
   // Create a reader that will return log records from "*file".
   // "*file" must remain live while this Reader is in use.
   //
-  // If "reporter" is non-NULL, it is notified whenever some data is
+  // If "reporter" is non-null, it is notified whenever some data is
   // dropped due to a detected corruption.  "*reporter" must remain
   // live while this Reader is in use.
   //
diff --git a/db/recovery_test.cc b/db/recovery_test.cc
index e5a7c80..c852803 100644
--- a/db/recovery_test.cc
+++ b/db/recovery_test.cc
@@ -17,7 +17,7 @@ namespace leveldb {
 
 class RecoveryTest {
  public:
-  RecoveryTest() : env_(Env::Default()), db_(NULL) {
+  RecoveryTest() : env_(Env::Default()), db_(nullptr) {
     dbname_ = test::TmpDir() + "/recovery_test";
     DestroyDB(dbname_, Options());
     Open();
@@ -44,25 +44,25 @@ class RecoveryTest {
 
   void Close() {
     delete db_;
-    db_ = NULL;
+    db_ = nullptr;
   }
 
-  Status OpenWithStatus(Options* options = NULL) {
+  Status OpenWithStatus(Options* options = nullptr) {
     Close();
     Options opts;
-    if (options != NULL) {
+    if (options != nullptr) {
       opts = *options;
     } else {
       opts.reuse_logs = true;  // TODO(sanjay): test both ways
       opts.create_if_missing = true;
     }
-    if (opts.env == NULL) {
+    if (opts.env == nullptr) {
       opts.env = env_;
     }
     return DB::Open(opts, dbname_, &db_);
   }
 
-  void Open(Options* options = NULL) {
+  void Open(Options* options = nullptr) {
     ASSERT_OK(OpenWithStatus(options));
     ASSERT_EQ(1, NumLogs());
   }
@@ -71,7 +71,7 @@ class RecoveryTest {
     return db_->Put(WriteOptions(), k, v);
   }
 
-  std::string Get(const std::string& k, const Snapshot* snapshot = NULL) {
+  std::string Get(const std::string& k, const Snapshot* snapshot = nullptr) {
     std::string result;
     Status s = db_->Get(ReadOptions(), k, &result);
     if (s.IsNotFound()) {
diff --git a/db/repair.cc b/db/repair.cc
index c10da82..df8dcd2 100644
--- a/db/repair.cc
+++ b/db/repair.cc
@@ -227,7 +227,7 @@ class Repairer {
     status = BuildTable(dbname_, env_, options_, table_cache_, iter, &meta);
     delete iter;
     mem->Unref();
-    mem = NULL;
+    mem = nullptr;
     if (status.ok()) {
       if (meta.file_size > 0) {
         table_numbers_.push_back(meta.number);
@@ -350,13 +350,13 @@ class Repairer {
       }
     }
     delete builder;
-    builder = NULL;
+    builder = nullptr;
 
     if (s.ok()) {
       s = file->Close();
     }
     delete file;
-    file = NULL;
+    file = nullptr;
 
     if (counter > 0 && s.ok()) {
       std::string orig = TableFileName(dbname_, t.meta.number);
@@ -410,7 +410,7 @@ class Repairer {
       status = file->Close();
     }
     delete file;
-    file = NULL;
+    file = nullptr;
 
     if (!status.ok()) {
       env_->DeleteFile(tmp);
@@ -438,14 +438,14 @@ class Repairer {
     //    dir/lost/foo
     const char* slash = strrchr(fname.c_str(), '/');
     std::string new_dir;
-    if (slash != NULL) {
+    if (slash != nullptr) {
       new_dir.assign(fname.data(), slash - fname.data());
     }
     new_dir.append("/lost");
     env_->CreateDir(new_dir);  // Ignore error
     std::string new_file = new_dir;
     new_file.append("/");
-    new_file.append((slash == NULL) ? fname.c_str() : slash + 1);
+    new_file.append((slash == nullptr) ? fname.c_str() : slash + 1);
     Status s = env_->RenameFile(fname, new_file);
     Log(options_.info_log, "Archiving %s: %s\n",
         fname.c_str(), s.ToString().c_str());
diff --git a/db/skiplist.h b/db/skiplist.h
index 8bd7776..b806ce0 100644
--- a/db/skiplist.h
+++ b/db/skiplist.h
@@ -123,9 +123,9 @@ class SkipList {
   bool KeyIsAfterNode(const Key& key, Node* n) const;
 
   // Return the earliest node that comes at or after key.
-  // Return NULL if there is no such node.
+  // Return nullptr if there is no such node.
   //
-  // If prev is non-NULL, fills prev[level] with pointer to previous
+  // If prev is non-null, fills prev[level] with pointer to previous
   // node at "level" for every level in [0..max_height_-1].
   Node* FindGreaterOrEqual(const Key& key, Node** prev) const;
 
@@ -190,12 +190,12 @@ SkipList<Key,Comparator>::NewNode(const Key& key, int height) {
 template<typename Key, class Comparator>
 inline SkipList<Key,Comparator>::Iterator::Iterator(const SkipList* list) {
   list_ = list;
-  node_ = NULL;
+  node_ = nullptr;
 }
 
 template<typename Key, class Comparator>
 inline bool SkipList<Key,Comparator>::Iterator::Valid() const {
-  return node_ != NULL;
+  return node_ != nullptr;
 }
 
 template<typename Key, class Comparator>
@@ -217,13 +217,13 @@ inline void SkipList<Key,Comparator>::Iterator::Prev() {
   assert(Valid());
   node_ = list_->FindLessThan(node_->key);
   if (node_ == list_->head_) {
-    node_ = NULL;
+    node_ = nullptr;
   }
 }
 
 template<typename Key, class Comparator>
 inline void SkipList<Key,Comparator>::Iterator::Seek(const Key& target) {
-  node_ = list_->FindGreaterOrEqual(target, NULL);
+  node_ = list_->FindGreaterOrEqual(target, nullptr);
 }
 
 template<typename Key, class Comparator>
@@ -235,7 +235,7 @@ template<typename Key, class Comparator>
 inline void SkipList<Key,Comparator>::Iterator::SeekToLast() {
   node_ = list_->FindLast();
   if (node_ == list_->head_) {
-    node_ = NULL;
+    node_ = nullptr;
   }
 }
 
@@ -254,8 +254,8 @@ int SkipList<Key,Comparator>::RandomHeight() {
 
 template<typename Key, class Comparator>
 bool SkipList<Key,Comparator>::KeyIsAfterNode(const Key& key, Node* n) const {
-  // NULL n is considered infinite
-  return (n != NULL) && (compare_(n->key, key) < 0);
+  // null n is considered infinite
+  return (n != nullptr) && (compare_(n->key, key) < 0);
 }
 
 template<typename Key, class Comparator>
@@ -269,7 +269,7 @@ typename SkipList<Key,Comparator>::Node* SkipList<Key,Comparator>::FindGreaterOr
       // Keep searching in this list
       x = next;
     } else {
-      if (prev != NULL) prev[level] = x;
+      if (prev != nullptr) prev[level] = x;
       if (level == 0) {
         return next;
       } else {
@@ -288,7 +288,7 @@ SkipList<Key,Comparator>::FindLessThan(const Key& key) const {
   while (true) {
     assert(x == head_ || compare_(x->key, key) < 0);
     Node* next = x->Next(level);
-    if (next == NULL || compare_(next->key, key) >= 0) {
+    if (next == nullptr || compare_(next->key, key) >= 0) {
       if (level == 0) {
         return x;
       } else {
@@ -308,7 +308,7 @@ typename SkipList<Key,Comparator>::Node* SkipList<Key,Comparator>::FindLast()
   int level = GetMaxHeight() - 1;
   while (true) {
     Node* next = x->Next(level);
-    if (next == NULL) {
+    if (next == nullptr) {
       if (level == 0) {
         return x;
       } else {
@@ -329,7 +329,7 @@ SkipList<Key,Comparator>::SkipList(Comparator cmp, Arena* arena)
       max_height_(reinterpret_cast<void*>(1)),
       rnd_(0xdeadbeef) {
   for (int i = 0; i < kMaxHeight; i++) {
-    head_->SetNext(i, NULL);
+    head_->SetNext(i, nullptr);
   }
 }
 
@@ -341,7 +341,7 @@ void SkipList<Key,Comparator>::Insert(const Key& key) {
   Node* x = FindGreaterOrEqual(key, prev);
 
   // Our data structure does not allow duplicate insertion
-  assert(x == NULL || !Equal(key, x->key));
+  assert(x == nullptr || !Equal(key, x->key));
 
   int height = RandomHeight();
   if (height > GetMaxHeight()) {
@@ -353,9 +353,9 @@ void SkipList<Key,Comparator>::Insert(const Key& key) {
     // It is ok to mutate max_height_ without any synchronization
     // with concurrent readers.  A concurrent reader that observes
     // the new value of max_height_ will see either the old value of
-    // new level pointers from head_ (NULL), or a new value set in
+    // new level pointers from head_ (nullptr), or a new value set in
     // the loop below.  In the former case the reader will
-    // immediately drop to the next level since NULL sorts after all
+    // immediately drop to the next level since nullptr sorts after all
     // keys.  In the latter case the reader will use the new node.
     max_height_.NoBarrier_Store(reinterpret_cast<void*>(height));
   }
@@ -371,8 +371,8 @@ void SkipList<Key,Comparator>::Insert(const Key& key) {
 
 template<typename Key, class Comparator>
 bool SkipList<Key,Comparator>::Contains(const Key& key) const {
-  Node* x = FindGreaterOrEqual(key, NULL);
-  if (x != NULL && Equal(key, x->key)) {
+  Node* x = FindGreaterOrEqual(key, nullptr);
+  if (x != nullptr && Equal(key, x->key)) {
     return true;
   } else {
     return false;
diff --git a/db/skiplist_test.cc b/db/skiplist_test.cc
index 90f9d0e..24e0887 100644
--- a/db/skiplist_test.cc
+++ b/db/skiplist_test.cc
@@ -310,7 +310,7 @@ class TestState {
 
   explicit TestState(int s)
       : seed_(s),
-        quit_flag_(NULL),
+        quit_flag_(nullptr),
         state_(STARTING),
         state_cv_(&mu_) {}
 
@@ -362,7 +362,7 @@ static void RunConcurrent(int run) {
     for (int i = 0; i < kSize; i++) {
       state.t_.WriteStep(&rnd);
     }
-    state.quit_flag_.Release_Store(&state);  // Any non-NULL arg will do
+    state.quit_flag_.Release_Store(&state);  // Any non-null arg will do
     state.Wait(TestState::DONE);
   }
 }
diff --git a/db/table_cache.cc b/db/table_cache.cc
index 6cf005b..7226d3b 100644
--- a/db/table_cache.cc
+++ b/db/table_cache.cc
@@ -49,10 +49,10 @@ Status TableCache::FindTable(uint64_t file_number, uint64_t file_size,
   EncodeFixed64(buf, file_number);
   Slice key(buf, sizeof(buf));
   *handle = cache_->Lookup(key);
-  if (*handle == NULL) {
+  if (*handle == nullptr) {
     std::string fname = TableFileName(dbname_, file_number);
-    RandomAccessFile* file = NULL;
-    Table* table = NULL;
+    RandomAccessFile* file = nullptr;
+    Table* table = nullptr;
     s = env_->NewRandomAccessFile(fname, &file);
     if (!s.ok()) {
       std::string old_fname = SSTTableFileName(dbname_, file_number);
@@ -65,7 +65,7 @@ Status TableCache::FindTable(uint64_t file_number, uint64_t file_size,
     }
 
     if (!s.ok()) {
-      assert(table == NULL);
+      assert(table == nullptr);
       delete file;
       // We do not cache error results so that if the error is transient,
       // or somebody repairs the file, we recover automatically.
@@ -83,11 +83,11 @@ Iterator* TableCache::NewIterator(const ReadOptions& options,
                                   uint64_t file_number,
                                   uint64_t file_size,
                                   Table** tableptr) {
-  if (tableptr != NULL) {
-    *tableptr = NULL;
+  if (tableptr != nullptr) {
+    *tableptr = nullptr;
   }
 
-  Cache::Handle* handle = NULL;
+  Cache::Handle* handle = nullptr;
   Status s = FindTable(file_number, file_size, &handle);
   if (!s.ok()) {
     return NewErrorIterator(s);
@@ -96,7 +96,7 @@ Iterator* TableCache::NewIterator(const ReadOptions& options,
   Table* table = reinterpret_cast<TableAndFile*>(cache_->Value(handle))->table;
   Iterator* result = table->NewIterator(options);
   result->RegisterCleanup(&UnrefEntry, cache_, handle);
-  if (tableptr != NULL) {
+  if (tableptr != nullptr) {
     *tableptr = table;
   }
   return result;
@@ -108,7 +108,7 @@ Status TableCache::Get(const ReadOptions& options,
                        const Slice& k,
                        void* arg,
                        void (*saver)(void*, const Slice&, const Slice&)) {
-  Cache::Handle* handle = NULL;
+  Cache::Handle* handle = nullptr;
   Status s = FindTable(file_number, file_size, &handle);
   if (s.ok()) {
     Table* t = reinterpret_cast<TableAndFile*>(cache_->Value(handle))->table;
diff --git a/db/table_cache.h b/db/table_cache.h
index e9191dc..ae8bee5 100644
--- a/db/table_cache.h
+++ b/db/table_cache.h
@@ -25,15 +25,15 @@ class TableCache {
 
   // Return an iterator for the specified file number (the corresponding
   // file length must be exactly "file_size" bytes).  If "tableptr" is
-  // non-NULL, also sets "*tableptr" to point to the Table object
-  // underlying the returned iterator, or NULL if no Table object underlies
-  // the returned iterator.  The returned "*tableptr" object is owned by
-  // the cache and should not be deleted, and is valid for as long as the
+  // non-null, also sets "*tableptr" to point to the Table object
+  // underlying the returned iterator, or to nullptr if no Table object
+  // underlies the returned iterator.  The returned "*tableptr" object is owned
+  // by the cache and should not be deleted, and is valid for as long as the
   // returned iterator is live.
   Iterator* NewIterator(const ReadOptions& options,
                         uint64_t file_number,
                         uint64_t file_size,
-                        Table** tableptr = NULL);
+                        Table** tableptr = nullptr);
 
   // If a seek to internal key "k" in specified file finds an entry,
   // call (*handle_result)(arg, found_key, found_value).
diff --git a/db/version_edit.cc b/db/version_edit.cc
index f10a2d5..b7a366d 100644
--- a/db/version_edit.cc
+++ b/db/version_edit.cc
@@ -109,7 +109,7 @@ static bool GetLevel(Slice* input, int* level) {
 Status VersionEdit::DecodeFrom(const Slice& src) {
   Clear();
   Slice input = src;
-  const char* msg = NULL;
+  const char* msg = nullptr;
   uint32_t tag;
 
   // Temporary storage for parsing
@@ -119,7 +119,7 @@ Status VersionEdit::DecodeFrom(const Slice& src) {
   Slice str;
   InternalKey key;
 
-  while (msg == NULL && GetVarint32(&input, &tag)) {
+  while (msg == nullptr && GetVarint32(&input, &tag)) {
     switch (tag) {
       case kComparator:
         if (GetLengthPrefixedSlice(&input, &str)) {
@@ -198,12 +198,12 @@ Status VersionEdit::DecodeFrom(const Slice& src) {
     }
   }
 
-  if (msg == NULL && !input.empty()) {
+  if (msg == nullptr && !input.empty()) {
     msg = "invalid tag";
   }
 
   Status result;
-  if (msg != NULL) {
+  if (msg != nullptr) {
     result = Status::Corruption("VersionEdit", msg);
   }
   return result;
diff --git a/db/version_set.cc b/db/version_set.cc
index 7022b27..02cc66f 100644
--- a/db/version_set.cc
+++ b/db/version_set.cc
@@ -106,15 +106,15 @@ int FindFile(const InternalKeyComparator& icmp,
 
 static bool AfterFile(const Comparator* ucmp,
                       const Slice* user_key, const FileMetaData* f) {
-  // NULL user_key occurs before all keys and is therefore never after *f
-  return (user_key != NULL &&
+  // null user_key occurs before all keys and is therefore never after *f
+  return (user_key != nullptr &&
           ucmp->Compare(*user_key, f->largest.user_key()) > 0);
 }
 
 static bool BeforeFile(const Comparator* ucmp,
                        const Slice* user_key, const FileMetaData* f) {
-  // NULL user_key occurs after all keys and is therefore never before *f
-  return (user_key != NULL &&
+  // null user_key occurs after all keys and is therefore never before *f
+  return (user_key != nullptr &&
           ucmp->Compare(*user_key, f->smallest.user_key()) < 0);
 }
 
@@ -141,7 +141,7 @@ bool SomeFileOverlapsRange(
 
   // Binary search over file list
   uint32_t index = 0;
-  if (smallest_user_key != NULL) {
+  if (smallest_user_key != nullptr) {
     // Find the earliest possible internal key for smallest_user_key
     InternalKey small(*smallest_user_key, kMaxSequenceNumber,kValueTypeForSeek);
     index = FindFile(icmp, files, small.Encode());
@@ -338,9 +338,9 @@ Status Version::Get(const ReadOptions& options,
   const Comparator* ucmp = vset_->icmp_.user_comparator();
   Status s;
 
-  stats->seek_file = NULL;
+  stats->seek_file = nullptr;
   stats->seek_file_level = -1;
-  FileMetaData* last_file_read = NULL;
+  FileMetaData* last_file_read = nullptr;
   int last_file_read_level = -1;
 
   // We can search level-by-level since entries never hop across
@@ -374,13 +374,13 @@ Status Version::Get(const ReadOptions& options,
       // Binary search to find earliest index whose largest key >= ikey.
       uint32_t index = FindFile(vset_->icmp_, files_[level], ikey);
       if (index >= num_files) {
-        files = NULL;
+        files = nullptr;
         num_files = 0;
       } else {
         tmp2 = files[index];
         if (ucmp->Compare(user_key, tmp2->smallest.user_key()) < 0) {
           // All of "tmp2" is past any data for user_key
-          files = NULL;
+          files = nullptr;
           num_files = 0;
         } else {
           files = &tmp2;
@@ -390,7 +390,7 @@ Status Version::Get(const ReadOptions& options,
     }
 
     for (uint32_t i = 0; i < num_files; ++i) {
-      if (last_file_read != NULL && stats->seek_file == NULL) {
+      if (last_file_read != nullptr && stats->seek_file == nullptr) {
         // We have had more than one seek for this read.  Charge the 1st file.
         stats->seek_file = last_file_read;
         stats->seek_file_level = last_file_read_level;
@@ -430,9 +430,9 @@ Status Version::Get(const ReadOptions& options,
 
 bool Version::UpdateStats(const GetStats& stats) {
   FileMetaData* f = stats.seek_file;
-  if (f != NULL) {
+  if (f != nullptr) {
     f->allowed_seeks--;
-    if (f->allowed_seeks <= 0 && file_to_compact_ == NULL) {
+    if (f->allowed_seeks <= 0 && file_to_compact_ == nullptr) {
       file_to_compact_ = f;
       file_to_compact_level_ = stats.seek_file_level;
       return true;
@@ -537,10 +537,10 @@ void Version::GetOverlappingInputs(
   assert(level < config::kNumLevels);
   inputs->clear();
   Slice user_begin, user_end;
-  if (begin != NULL) {
+  if (begin != nullptr) {
     user_begin = begin->user_key();
   }
-  if (end != NULL) {
+  if (end != nullptr) {
     user_end = end->user_key();
   }
   const Comparator* user_cmp = vset_->icmp_.user_comparator();
@@ -548,20 +548,21 @@ void Version::GetOverlappingInputs(
     FileMetaData* f = files_[level][i++];
     const Slice file_start = f->smallest.user_key();
     const Slice file_limit = f->largest.user_key();
-    if (begin != NULL && user_cmp->Compare(file_limit, user_begin) < 0) {
+    if (begin != nullptr && user_cmp->Compare(file_limit, user_begin) < 0) {
       // "f" is completely before specified range; skip it
-    } else if (end != NULL && user_cmp->Compare(file_start, user_end) > 0) {
+    } else if (end != nullptr && user_cmp->Compare(file_start, user_end) > 0) {
       // "f" is completely after specified range; skip it
     } else {
       inputs->push_back(f);
       if (level == 0) {
         // Level-0 files may overlap each other.  So check if the newly
         // added file has expanded the range.  If so, restart search.
-        if (begin != NULL && user_cmp->Compare(file_start, user_begin) < 0) {
+        if (begin != nullptr && user_cmp->Compare(file_start, user_begin) < 0) {
           user_begin = file_start;
           inputs->clear();
           i = 0;
-        } else if (end != NULL && user_cmp->Compare(file_limit, user_end) > 0) {
+        } else if (end != nullptr && user_cmp->Compare(file_limit,
+                                                       user_end) > 0) {
           user_end = file_limit;
           inputs->clear();
           i = 0;
@@ -786,10 +787,10 @@ VersionSet::VersionSet(const std::string& dbname,
       last_sequence_(0),
       log_number_(0),
       prev_log_number_(0),
-      descriptor_file_(NULL),
-      descriptor_log_(NULL),
+      descriptor_file_(nullptr),
+      descriptor_log_(nullptr),
       dummy_versions_(this),
-      current_(NULL) {
+      current_(nullptr) {
   AppendVersion(new Version(this));
 }
 
@@ -804,7 +805,7 @@ void VersionSet::AppendVersion(Version* v) {
   // Make "v" current
   assert(v->refs_ == 0);
   assert(v != current_);
-  if (current_ != NULL) {
+  if (current_ != nullptr) {
     current_->Unref();
   }
   current_ = v;
@@ -844,10 +845,10 @@ Status VersionSet::LogAndApply(VersionEdit* edit, port::Mutex* mu) {
   // a temporary file that contains a snapshot of the current version.
   std::string new_manifest_file;
   Status s;
-  if (descriptor_log_ == NULL) {
+  if (descriptor_log_ == nullptr) {
     // No reason to unlock *mu here since we only hit this path in the
     // first call to LogAndApply (when opening the database).
-    assert(descriptor_file_ == NULL);
+    assert(descriptor_file_ == nullptr);
     new_manifest_file = DescriptorFileName(dbname_, manifest_file_number_);
     edit->SetNextFile(next_file_number_);
     s = env_->NewWritableFile(new_manifest_file, &descriptor_file_);
@@ -893,8 +894,8 @@ Status VersionSet::LogAndApply(VersionEdit* edit, port::Mutex* mu) {
     if (!new_manifest_file.empty()) {
       delete descriptor_log_;
       delete descriptor_file_;
-      descriptor_log_ = NULL;
-      descriptor_file_ = NULL;
+      descriptor_log_ = nullptr;
+      descriptor_file_ = nullptr;
       env_->DeleteFile(new_manifest_file);
     }
   }
@@ -986,7 +987,7 @@ Status VersionSet::Recover(bool *save_manifest) {
     }
   }
   delete file;
-  file = NULL;
+  file = nullptr;
 
   if (s.ok()) {
     if (!have_next_file) {
@@ -1044,12 +1045,12 @@ bool VersionSet::ReuseManifest(const std::string& dscname,
     return false;
   }
 
-  assert(descriptor_file_ == NULL);
-  assert(descriptor_log_ == NULL);
+  assert(descriptor_file_ == nullptr);
+  assert(descriptor_log_ == nullptr);
   Status r = env_->NewAppendableFile(dscname, &descriptor_file_);
   if (!r.ok()) {
     Log(options_->info_log, "Reuse MANIFEST: %s\n", r.ToString().c_str());
-    assert(descriptor_file_ == NULL);
+    assert(descriptor_file_ == nullptr);
     return false;
   }
 
@@ -1176,7 +1177,7 @@ uint64_t VersionSet::ApproximateOffsetOf(Version* v, const InternalKey& ikey) {
         Table* tableptr;
         Iterator* iter = table_cache_->NewIterator(
             ReadOptions(), files[i]->number, files[i]->file_size, &tableptr);
-        if (tableptr != NULL) {
+        if (tableptr != nullptr) {
           result += tableptr->ApproximateOffsetOf(ikey.Encode());
         }
         delete iter;
@@ -1299,7 +1300,7 @@ Compaction* VersionSet::PickCompaction() {
   // We prefer compactions triggered by too much data in a level over
   // the compactions triggered by seeks.
   const bool size_compaction = (current_->compaction_score_ >= 1);
-  const bool seek_compaction = (current_->file_to_compact_ != NULL);
+  const bool seek_compaction = (current_->file_to_compact_ != nullptr);
   if (size_compaction) {
     level = current_->compaction_level_;
     assert(level >= 0);
@@ -1324,7 +1325,7 @@ Compaction* VersionSet::PickCompaction() {
     c = new Compaction(options_, level);
     c->inputs_[0].push_back(current_->file_to_compact_);
   } else {
-    return NULL;
+    return nullptr;
   }
 
   c->input_version_ = current_;
@@ -1414,7 +1415,7 @@ Compaction* VersionSet::CompactRange(
   std::vector<FileMetaData*> inputs;
   current_->GetOverlappingInputs(level, begin, end, &inputs);
   if (inputs.empty()) {
-    return NULL;
+    return nullptr;
   }
 
   // Avoid compacting too much in one shot in case the range is large.
@@ -1445,7 +1446,7 @@ Compaction* VersionSet::CompactRange(
 Compaction::Compaction(const Options* options, int level)
     : level_(level),
       max_output_file_size_(MaxFileSizeForLevel(options, level)),
-      input_version_(NULL),
+      input_version_(nullptr),
       grandparent_index_(0),
       seen_key_(false),
       overlapped_bytes_(0) {
@@ -1455,7 +1456,7 @@ Compaction::Compaction(const Options* options, int level)
 }
 
 Compaction::~Compaction() {
-  if (input_version_ != NULL) {
+  if (input_version_ != nullptr) {
     input_version_->Unref();
   }
 }
@@ -1523,9 +1524,9 @@ bool Compaction::ShouldStopBefore(const Slice& internal_key) {
 }
 
 void Compaction::ReleaseInputs() {
-  if (input_version_ != NULL) {
+  if (input_version_ != nullptr) {
     input_version_->Unref();
-    input_version_ = NULL;
+    input_version_ = nullptr;
   }
 }
 
diff --git a/db/version_set.h b/db/version_set.h
index 80d448a..77b9895 100644
--- a/db/version_set.h
+++ b/db/version_set.h
@@ -45,8 +45,8 @@ int FindFile(const InternalKeyComparator& icmp,
 
 // Returns true iff some file in "files" overlaps the user key range
 // [*smallest,*largest].
-// smallest==NULL represents a key smaller than all keys in the DB.
-// largest==NULL represents a key largest than all keys in the DB.
+// smallest==nullptr represents a key smaller than all keys in the DB.
+// largest==nullptr represents a key largest than all keys in the DB.
 // REQUIRES: If disjoint_sorted_files, files[] contains disjoint ranges
 //           in sorted order.
 bool SomeFileOverlapsRange(const InternalKeyComparator& icmp,
@@ -90,14 +90,14 @@ class Version {
 
   void GetOverlappingInputs(
       int level,
-      const InternalKey* begin,         // NULL means before all keys
-      const InternalKey* end,           // NULL means after all keys
+      const InternalKey* begin,         // nullptr means before all keys
+      const InternalKey* end,           // nullptr means after all keys
       std::vector<FileMetaData*>* inputs);
 
   // Returns true iff some file in the specified level overlaps
   // some part of [*smallest_user_key,*largest_user_key].
-  // smallest_user_key==NULL represents a key smaller than all keys in the DB.
-  // largest_user_key==NULL represents a key largest than all keys in the DB.
+  // smallest_user_key==nullptr represents a key smaller than all the DB's keys.
+  // largest_user_key==nullptr represents a key largest than all the DB's keys.
   bool OverlapInLevel(int level,
                       const Slice* smallest_user_key,
                       const Slice* largest_user_key);
@@ -148,7 +148,7 @@ class Version {
 
   explicit Version(VersionSet* vset)
       : vset_(vset), next_(this), prev_(this), refs_(0),
-        file_to_compact_(NULL),
+        file_to_compact_(nullptr),
         file_to_compact_level_(-1),
         compaction_score_(-1),
         compaction_level_(-1) {
@@ -224,13 +224,13 @@ class VersionSet {
   uint64_t PrevLogNumber() const { return prev_log_number_; }
 
   // Pick level and inputs for a new compaction.
-  // Returns NULL if there is no compaction to be done.
+  // Returns nullptr if there is no compaction to be done.
   // Otherwise returns a pointer to a heap-allocated object that
   // describes the compaction.  Caller should delete the result.
   Compaction* PickCompaction();
 
   // Return a compaction object for compacting the range [begin,end] in
-  // the specified level.  Returns NULL if there is nothing in that
+  // the specified level.  Returns nullptr if there is nothing in that
   // level that overlaps the specified range.  Caller should delete
   // the result.
   Compaction* CompactRange(
@@ -249,7 +249,7 @@ class VersionSet {
   // Returns true iff some level needs a compaction.
   bool NeedsCompaction() const {
     Version* v = current_;
-    return (v->compaction_score_ >= 1) || (v->file_to_compact_ != NULL);
+    return (v->compaction_score_ >= 1) || (v->file_to_compact_ != nullptr);
   }
 
   // Add all files listed in any live version to *live.
diff --git a/db/version_set_test.cc b/db/version_set_test.cc
index 501e34d..d21433e 100644
--- a/db/version_set_test.cc
+++ b/db/version_set_test.cc
@@ -40,20 +40,20 @@ class FindFileTest {
 
   bool Overlaps(const char* smallest, const char* largest) {
     InternalKeyComparator cmp(BytewiseComparator());
-    Slice s(smallest != NULL ? smallest : "");
-    Slice l(largest != NULL ? largest : "");
+    Slice s(smallest != nullptr ? smallest : "");
+    Slice l(largest != nullptr ? largest : "");
     return SomeFileOverlapsRange(cmp, disjoint_sorted_files_, files_,
-                                 (smallest != NULL ? &s : NULL),
-                                 (largest != NULL ? &l : NULL));
+                                 (smallest != nullptr ? &s : nullptr),
+                                 (largest != nullptr ? &l : nullptr));
   }
 };
 
 TEST(FindFileTest, Empty) {
   ASSERT_EQ(0, Find("foo"));
   ASSERT_TRUE(! Overlaps("a", "z"));
-  ASSERT_TRUE(! Overlaps(NULL, "z"));
-  ASSERT_TRUE(! Overlaps("a", NULL));
-  ASSERT_TRUE(! Overlaps(NULL, NULL));
+  ASSERT_TRUE(! Overlaps(nullptr, "z"));
+  ASSERT_TRUE(! Overlaps("a", nullptr));
+  ASSERT_TRUE(! Overlaps(nullptr, nullptr));
 }
 
 TEST(FindFileTest, Single) {
@@ -78,12 +78,12 @@ TEST(FindFileTest, Single) {
   ASSERT_TRUE(Overlaps("q", "q"));
   ASSERT_TRUE(Overlaps("q", "q1"));
 
-  ASSERT_TRUE(! Overlaps(NULL, "j"));
-  ASSERT_TRUE(! Overlaps("r", NULL));
-  ASSERT_TRUE(Overlaps(NULL, "p"));
-  ASSERT_TRUE(Overlaps(NULL, "p1"));
-  ASSERT_TRUE(Overlaps("q", NULL));
-  ASSERT_TRUE(Overlaps(NULL, NULL));
+  ASSERT_TRUE(! Overlaps(nullptr, "j"));
+  ASSERT_TRUE(! Overlaps("r", nullptr));
+  ASSERT_TRUE(Overlaps(nullptr, "p"));
+  ASSERT_TRUE(Overlaps(nullptr, "p1"));
+  ASSERT_TRUE(Overlaps("q", nullptr));
+  ASSERT_TRUE(Overlaps(nullptr, nullptr));
 }
 
 
@@ -130,19 +130,19 @@ TEST(FindFileTest, MultipleNullBoundaries) {
   Add("200", "250");
   Add("300", "350");
   Add("400", "450");
-  ASSERT_TRUE(! Overlaps(NULL, "149"));
-  ASSERT_TRUE(! Overlaps("451", NULL));
-  ASSERT_TRUE(Overlaps(NULL, NULL));
-  ASSERT_TRUE(Overlaps(NULL, "150"));
-  ASSERT_TRUE(Overlaps(NULL, "199"));
-  ASSERT_TRUE(Overlaps(NULL, "200"));
-  ASSERT_TRUE(Overlaps(NULL, "201"));
-  ASSERT_TRUE(Overlaps(NULL, "400"));
-  ASSERT_TRUE(Overlaps(NULL, "800"));
-  ASSERT_TRUE(Overlaps("100", NULL));
-  ASSERT_TRUE(Overlaps("200", NULL));
-  ASSERT_TRUE(Overlaps("449", NULL));
-  ASSERT_TRUE(Overlaps("450", NULL));
+  ASSERT_TRUE(! Overlaps(nullptr, "149"));
+  ASSERT_TRUE(! Overlaps("451", nullptr));
+  ASSERT_TRUE(Overlaps(nullptr, nullptr));
+  ASSERT_TRUE(Overlaps(nullptr, "150"));
+  ASSERT_TRUE(Overlaps(nullptr, "199"));
+  ASSERT_TRUE(Overlaps(nullptr, "200"));
+  ASSERT_TRUE(Overlaps(nullptr, "201"));
+  ASSERT_TRUE(Overlaps(nullptr, "400"));
+  ASSERT_TRUE(Overlaps(nullptr, "800"));
+  ASSERT_TRUE(Overlaps("100", nullptr));
+  ASSERT_TRUE(Overlaps("200", nullptr));
+  ASSERT_TRUE(Overlaps("449", nullptr));
+  ASSERT_TRUE(Overlaps("450", nullptr));
 }
 
 TEST(FindFileTest, OverlapSequenceChecks) {
diff --git a/doc/bench/db_bench_sqlite3.cc b/doc/bench/db_bench_sqlite3.cc
index e63aaa8..7e05de2 100644
--- a/doc/bench/db_bench_sqlite3.cc
+++ b/doc/bench/db_bench_sqlite3.cc
@@ -76,7 +76,7 @@ static bool FLAGS_transaction = true;
 static bool FLAGS_WAL_enabled = true;
 
 // Use the db with the following name.
-static const char* FLAGS_db = NULL;
+static const char* FLAGS_db = nullptr;
 
 inline
 static void ExecErrorCheck(int status, char *err_msg) {
@@ -107,7 +107,8 @@ inline
 static void WalCheckpoint(sqlite3* db_) {
   // Flush all writes to disk
   if (FLAGS_WAL_enabled) {
-    sqlite3_wal_checkpoint_v2(db_, NULL, SQLITE_CHECKPOINT_FULL, NULL, NULL);
+    sqlite3_wal_checkpoint_v2(db_, nullptr, SQLITE_CHECKPOINT_FULL, nullptr,
+                              nullptr);
   }
 }
 
@@ -207,18 +208,18 @@ class Benchmark {
     fprintf(stderr, "SQLite:     version %s\n", SQLITE_VERSION);
 
 #if defined(__linux)
-    time_t now = time(NULL);
+    time_t now = time(nullptr);
     fprintf(stderr, "Date:       %s", ctime(&now));  // ctime() adds newline
 
     FILE* cpuinfo = fopen("/proc/cpuinfo", "r");
-    if (cpuinfo != NULL) {
+    if (cpuinfo != nullptr) {
       char line[1000];
       int num_cpus = 0;
       std::string cpu_type;
       std::string cache_size;
-      while (fgets(line, sizeof(line), cpuinfo) != NULL) {
+      while (fgets(line, sizeof(line), cpuinfo) != nullptr) {
         const char* sep = strchr(line, ':');
-        if (sep == NULL) {
+        if (sep == nullptr) {
           continue;
         }
         Slice key = TrimSpace(Slice(line, sep - 1 - line));
@@ -313,7 +314,7 @@ class Benchmark {
   };
 
   Benchmark()
-  : db_(NULL),
+  : db_(nullptr),
     db_num_(0),
     num_(FLAGS_num),
     reads_(FLAGS_reads < 0 ? FLAGS_num : FLAGS_reads),
@@ -345,12 +346,12 @@ class Benchmark {
     Open();
 
     const char* benchmarks = FLAGS_benchmarks;
-    while (benchmarks != NULL) {
+    while (benchmarks != nullptr) {
       const char* sep = strchr(benchmarks, ',');
       Slice name;
-      if (sep == NULL) {
+      if (sep == nullptr) {
         name = benchmarks;
-        benchmarks = NULL;
+        benchmarks = nullptr;
       } else {
         name = Slice(benchmarks, sep - benchmarks);
         benchmarks = sep + 1;
@@ -415,11 +416,11 @@ class Benchmark {
   }
 
   void Open() {
-    assert(db_ == NULL);
+    assert(db_ == nullptr);
 
     int status;
     char file_name[100];
-    char* err_msg = NULL;
+    char* err_msg = nullptr;
     db_num_++;
 
     // Open database
@@ -439,7 +440,7 @@ class Benchmark {
     char cache_size[100];
     snprintf(cache_size, sizeof(cache_size), "PRAGMA cache_size = %d",
              FLAGS_num_pages);
-    status = sqlite3_exec(db_, cache_size, NULL, NULL, &err_msg);
+    status = sqlite3_exec(db_, cache_size, nullptr, nullptr, &err_msg);
     ExecErrorCheck(status, err_msg);
 
     // FLAGS_page_size is defaulted to 1024
@@ -447,7 +448,7 @@ class Benchmark {
       char page_size[100];
       snprintf(page_size, sizeof(page_size), "PRAGMA page_size = %d",
                FLAGS_page_size);
-      status = sqlite3_exec(db_, page_size, NULL, NULL, &err_msg);
+      status = sqlite3_exec(db_, page_size, nullptr, nullptr, &err_msg);
       ExecErrorCheck(status, err_msg);
     }
 
@@ -457,9 +458,10 @@ class Benchmark {
 
       // LevelDB's default cache size is a combined 4 MB
       std::string WAL_checkpoint = "PRAGMA wal_autocheckpoint = 4096";
-      status = sqlite3_exec(db_, WAL_stmt.c_str(), NULL, NULL, &err_msg);
+      status = sqlite3_exec(db_, WAL_stmt.c_str(), nullptr, nullptr, &err_msg);
       ExecErrorCheck(status, err_msg);
-      status = sqlite3_exec(db_, WAL_checkpoint.c_str(), NULL, NULL, &err_msg);
+      status = sqlite3_exec(db_, WAL_checkpoint.c_str(), nullptr, nullptr,
+                            &err_msg);
       ExecErrorCheck(status, err_msg);
     }
 
@@ -470,7 +472,8 @@ class Benchmark {
     std::string stmt_array[] = { locking_stmt, create_stmt };
     int stmt_array_length = sizeof(stmt_array) / sizeof(std::string);
     for (int i = 0; i < stmt_array_length; i++) {
-      status = sqlite3_exec(db_, stmt_array[i].c_str(), NULL, NULL, &err_msg);
+      status = sqlite3_exec(db_, stmt_array[i].c_str(), nullptr, nullptr,
+                            &err_msg);
       ExecErrorCheck(status, err_msg);
     }
   }
@@ -484,7 +487,7 @@ class Benchmark {
         return;
       }
       sqlite3_close(db_);
-      db_ = NULL;
+      db_ = nullptr;
       Open();
       Start();
     }
@@ -495,7 +498,7 @@ class Benchmark {
       message_ = msg;
     }
 
-    char* err_msg = NULL;
+    char* err_msg = nullptr;
     int status;
 
     sqlite3_stmt *replace_stmt, *begin_trans_stmt, *end_trans_stmt;
@@ -506,18 +509,18 @@ class Benchmark {
     // Check for synchronous flag in options
     std::string sync_stmt = (write_sync) ? "PRAGMA synchronous = FULL" :
                                            "PRAGMA synchronous = OFF";
-    status = sqlite3_exec(db_, sync_stmt.c_str(), NULL, NULL, &err_msg);
+    status = sqlite3_exec(db_, sync_stmt.c_str(), nullptr, nullptr, &err_msg);
     ExecErrorCheck(status, err_msg);
 
     // Preparing sqlite3 statements
     status = sqlite3_prepare_v2(db_, replace_str.c_str(), -1,
-                                &replace_stmt, NULL);
+                                &replace_stmt, nullptr);
     ErrorCheck(status);
     status = sqlite3_prepare_v2(db_, begin_trans_str.c_str(), -1,
-                                &begin_trans_stmt, NULL);
+                                &begin_trans_stmt, nullptr);
     ErrorCheck(status);
     status = sqlite3_prepare_v2(db_, end_trans_str.c_str(), -1,
-                                &end_trans_stmt, NULL);
+                                &end_trans_stmt, nullptr);
     ErrorCheck(status);
 
     bool transaction = (entries_per_batch > 1);
@@ -588,12 +591,12 @@ class Benchmark {
 
     // Preparing sqlite3 statements
     status = sqlite3_prepare_v2(db_, begin_trans_str.c_str(), -1,
-                                &begin_trans_stmt, NULL);
+                                &begin_trans_stmt, nullptr);
     ErrorCheck(status);
     status = sqlite3_prepare_v2(db_, end_trans_str.c_str(), -1,
-                                &end_trans_stmt, NULL);
+                                &end_trans_stmt, nullptr);
     ErrorCheck(status);
-    status = sqlite3_prepare_v2(db_, read_str.c_str(), -1, &read_stmt, NULL);
+    status = sqlite3_prepare_v2(db_, read_str.c_str(), -1, &read_stmt, nullptr);
     ErrorCheck(status);
 
     bool transaction = (entries_per_batch > 1);
@@ -651,7 +654,7 @@ class Benchmark {
     sqlite3_stmt *pStmt;
     std::string read_str = "SELECT * FROM test ORDER BY key";
 
-    status = sqlite3_prepare_v2(db_, read_str.c_str(), -1, &pStmt, NULL);
+    status = sqlite3_prepare_v2(db_, read_str.c_str(), -1, &pStmt, nullptr);
     ErrorCheck(status);
     for (int i = 0; i < reads_ && SQLITE_ROW == sqlite3_step(pStmt); i++) {
       bytes_ += sqlite3_column_bytes(pStmt, 1) + sqlite3_column_bytes(pStmt, 2);
@@ -706,7 +709,7 @@ int main(int argc, char** argv) {
   }
 
   // Choose a location for the test database if none given with --db=<path>
-  if (FLAGS_db == NULL) {
+  if (FLAGS_db == nullptr) {
       leveldb::Env::Default()->GetTestDirectory(&default_db_path);
       default_db_path += "/dbbench";
       FLAGS_db = default_db_path.c_str();
diff --git a/doc/bench/db_bench_tree_db.cc b/doc/bench/db_bench_tree_db.cc
index 4ca381f..9f8fb90 100644
--- a/doc/bench/db_bench_tree_db.cc
+++ b/doc/bench/db_bench_tree_db.cc
@@ -69,7 +69,7 @@ static bool FLAGS_use_existing_db = false;
 static bool FLAGS_compression = true;
 
 // Use the db with the following name.
-static const char* FLAGS_db = NULL;
+static const char* FLAGS_db = nullptr;
 
 inline
 static void DBSynchronize(kyotocabinet::TreeDB* db_)
@@ -183,18 +183,18 @@ class Benchmark {
             kyotocabinet::VERSION, kyotocabinet::LIBVER, kyotocabinet::LIBREV);
 
 #if defined(__linux)
-    time_t now = time(NULL);
+    time_t now = time(nullptr);
     fprintf(stderr, "Date:           %s", ctime(&now));  // ctime() adds newline
 
     FILE* cpuinfo = fopen("/proc/cpuinfo", "r");
-    if (cpuinfo != NULL) {
+    if (cpuinfo != nullptr) {
       char line[1000];
       int num_cpus = 0;
       std::string cpu_type;
       std::string cache_size;
-      while (fgets(line, sizeof(line), cpuinfo) != NULL) {
+      while (fgets(line, sizeof(line), cpuinfo) != nullptr) {
         const char* sep = strchr(line, ':');
-        if (sep == NULL) {
+        if (sep == nullptr) {
           continue;
         }
         Slice key = TrimSpace(Slice(line, sep - 1 - line));
@@ -289,7 +289,7 @@ class Benchmark {
   };
 
   Benchmark()
-  : db_(NULL),
+  : db_(nullptr),
     num_(FLAGS_num),
     reads_(FLAGS_reads < 0 ? FLAGS_num : FLAGS_reads),
     bytes_(0),
@@ -321,12 +321,12 @@ class Benchmark {
     Open(false);
 
     const char* benchmarks = FLAGS_benchmarks;
-    while (benchmarks != NULL) {
+    while (benchmarks != nullptr) {
       const char* sep = strchr(benchmarks, ',');
       Slice name;
-      if (sep == NULL) {
+      if (sep == nullptr) {
         name = benchmarks;
-        benchmarks = NULL;
+        benchmarks = nullptr;
       } else {
         name = Slice(benchmarks, sep - benchmarks);
         benchmarks = sep + 1;
@@ -387,7 +387,7 @@ class Benchmark {
 
  private:
     void Open(bool sync) {
-    assert(db_ == NULL);
+    assert(db_ == nullptr);
 
     // Initialize db_
     db_ = new kyotocabinet::TreeDB();
@@ -430,7 +430,7 @@ class Benchmark {
         return;
       }
       delete db_;
-      db_ = NULL;
+      db_ = nullptr;
       Open(sync);
       Start();  // Do not count time taken to destroy/open
     }
@@ -516,7 +516,7 @@ int main(int argc, char** argv) {
   }
 
   // Choose a location for the test database if none given with --db=<path>
-  if (FLAGS_db == NULL) {
+  if (FLAGS_db == nullptr) {
       leveldb::Env::Default()->GetTestDirectory(&default_db_path);
       default_db_path += "/dbbench";
       FLAGS_db = default_db_path.c_str();
diff --git a/helpers/memenv/memenv.cc b/helpers/memenv/memenv.cc
index 43b009d..d44627b 100644
--- a/helpers/memenv/memenv.cc
+++ b/helpers/memenv/memenv.cc
@@ -246,7 +246,7 @@ class InMemoryEnv : public EnvWrapper {
                                    SequentialFile** result) {
     MutexLock lock(&mutex_);
     if (file_map_.find(fname) == file_map_.end()) {
-      *result = NULL;
+      *result = nullptr;
       return Status::IOError(fname, "File not found");
     }
 
@@ -258,7 +258,7 @@ class InMemoryEnv : public EnvWrapper {
                                      RandomAccessFile** result) {
     MutexLock lock(&mutex_);
     if (file_map_.find(fname) == file_map_.end()) {
-      *result = NULL;
+      *result = nullptr;
       return Status::IOError(fname, "File not found");
     }
 
@@ -286,7 +286,7 @@ class InMemoryEnv : public EnvWrapper {
     MutexLock lock(&mutex_);
     FileState** sptr = &file_map_[fname];
     FileState* file = *sptr;
-    if (file == NULL) {
+    if (file == nullptr) {
       file = new FileState();
       file->Ref();
     }
diff --git a/include/leveldb/cache.h b/include/leveldb/cache.h
index 145ad69..e416ea5 100644
--- a/include/leveldb/cache.h
+++ b/include/leveldb/cache.h
@@ -56,7 +56,7 @@ class LEVELDB_EXPORT Cache {
   virtual Handle* Insert(const Slice& key, void* value, size_t charge,
                          void (*deleter)(const Slice& key, void* value)) = 0;
 
-  // If the cache has no mapping for "key", returns NULL.
+  // If the cache has no mapping for "key", returns nullptr.
   //
   // Else return a handle that corresponds to the mapping.  The caller
   // must call this->Release(handle) when the returned mapping is no
diff --git a/include/leveldb/db.h b/include/leveldb/db.h
index 092a154..84c32bc 100644
--- a/include/leveldb/db.h
+++ b/include/leveldb/db.h
@@ -47,7 +47,7 @@ class LEVELDB_EXPORT DB {
   // Open the database with the specified "name".
   // Stores a pointer to a heap-allocated database in *dbptr and returns
   // OK on success.
-  // Stores NULL in *dbptr and returns a non-OK status on error.
+  // Stores nullptr in *dbptr and returns a non-OK status on error.
   // Caller should delete *dbptr when it is no longer needed.
   static Status Open(const Options& options,
                      const std::string& name,
@@ -141,10 +141,10 @@ class LEVELDB_EXPORT DB {
   // needed to access the data.  This operation should typically only
   // be invoked by users who understand the underlying implementation.
   //
-  // begin==NULL is treated as a key before all keys in the database.
-  // end==NULL is treated as a key after all keys in the database.
+  // begin==nullptr is treated as a key before all keys in the database.
+  // end==nullptr is treated as a key after all keys in the database.
   // Therefore the following call will compact the entire database:
-  //    db->CompactRange(NULL, NULL);
+  //    db->CompactRange(nullptr, nullptr);
   virtual void CompactRange(const Slice* begin, const Slice* end) = 0;
 };
 
diff --git a/include/leveldb/env.h b/include/leveldb/env.h
index 54c9e3b..87dc06e 100644
--- a/include/leveldb/env.h
+++ b/include/leveldb/env.h
@@ -47,7 +47,7 @@ class LEVELDB_EXPORT Env {
 
   // Create a brand new sequentially-readable file with the specified name.
   // On success, stores a pointer to the new file in *result and returns OK.
-  // On failure stores NULL in *result and returns non-OK.  If the file does
+  // On failure stores nullptr in *result and returns non-OK.  If the file does
   // not exist, returns a non-OK status.  Implementations should return a
   // NotFound status when the file does not exist.
   //
@@ -57,7 +57,7 @@ class LEVELDB_EXPORT Env {
 
   // Create a brand new random access read-only file with the
   // specified name.  On success, stores a pointer to the new file in
-  // *result and returns OK.  On failure stores NULL in *result and
+  // *result and returns OK.  On failure stores nullptr in *result and
   // returns non-OK.  If the file does not exist, returns a non-OK
   // status.  Implementations should return a NotFound status when the file does
   // not exist.
@@ -69,7 +69,7 @@ class LEVELDB_EXPORT Env {
   // Create an object that writes to a new file with the specified
   // name.  Deletes any existing file with the same name and creates a
   // new file.  On success, stores a pointer to the new file in
-  // *result and returns OK.  On failure stores NULL in *result and
+  // *result and returns OK.  On failure stores nullptr in *result and
   // returns non-OK.
   //
   // The returned file will only be accessed by one thread at a time.
@@ -79,7 +79,7 @@ class LEVELDB_EXPORT Env {
   // Create an object that either appends to an existing file, or
   // writes to a new file (if the file does not exist to begin with).
   // On success, stores a pointer to the new file in *result and
-  // returns OK.  On failure stores NULL in *result and returns
+  // returns OK.  On failure stores nullptr in *result and returns
   // non-OK.
   //
   // The returned file will only be accessed by one thread at a time.
@@ -117,7 +117,7 @@ class LEVELDB_EXPORT Env {
                             const std::string& target) = 0;
 
   // Lock the specified file.  Used to prevent concurrent access to
-  // the same db by multiple processes.  On failure, stores NULL in
+  // the same db by multiple processes.  On failure, stores nullptr in
   // *lock and returns non-OK.
   //
   // On success, stores a pointer to the object that represents the
@@ -264,7 +264,7 @@ class LEVELDB_EXPORT FileLock {
   virtual ~FileLock();
 };
 
-// Log the specified data to *info_log if info_log is non-NULL.
+// Log the specified data to *info_log if info_log is non-null.
 void Log(Logger* info_log, const char* format, ...)
 #   if defined(__GNUC__) || defined(__clang__)
     __attribute__((__format__ (__printf__, 2, 3)))
diff --git a/include/leveldb/options.h b/include/leveldb/options.h
index 1c42921..b6ddbd8 100644
--- a/include/leveldb/options.h
+++ b/include/leveldb/options.h
@@ -63,9 +63,9 @@ struct LEVELDB_EXPORT Options {
   Env* env;
 
   // Any internal progress/error information generated by the db will
-  // be written to info_log if it is non-NULL, or to a file stored
-  // in the same directory as the DB contents if info_log is NULL.
-  // Default: NULL
+  // be written to info_log if it is non-null, or to a file stored
+  // in the same directory as the DB contents if info_log is null.
+  // Default: nullptr
   Logger* info_log;
 
   // -------------------
@@ -93,9 +93,9 @@ struct LEVELDB_EXPORT Options {
   // Control over blocks (user data is stored in a set of blocks, and
   // a block is the unit of reading from disk).
 
-  // If non-NULL, use the specified cache for blocks.
-  // If NULL, leveldb will automatically create and use an 8MB internal cache.
-  // Default: NULL
+  // If non-null, use the specified cache for blocks.
+  // If null, leveldb will automatically create and use an 8MB internal cache.
+  // Default: nullptr
   Cache* block_cache;
 
   // Approximate size of user data packed per block.  Note that the
@@ -147,11 +147,11 @@ struct LEVELDB_EXPORT Options {
   // Default: currently false, but may become true later.
   bool reuse_logs;
 
-  // If non-NULL, use the specified filter policy to reduce disk reads.
+  // If non-null, use the specified filter policy to reduce disk reads.
   // Many applications will benefit from passing the result of
   // NewBloomFilterPolicy() here.
   //
-  // Default: NULL
+  // Default: nullptr
   const FilterPolicy* filter_policy;
 
   // Create an Options object with default values for all fields.
@@ -170,17 +170,17 @@ struct LEVELDB_EXPORT ReadOptions {
   // Default: true
   bool fill_cache;
 
-  // If "snapshot" is non-NULL, read as of the supplied snapshot
+  // If "snapshot" is non-null, read as of the supplied snapshot
   // (which must belong to the DB that is being read and which must
-  // not have been released).  If "snapshot" is NULL, use an implicit
+  // not have been released).  If "snapshot" is null, use an implicit
   // snapshot of the state at the beginning of this read operation.
-  // Default: NULL
+  // Default: nullptr
   const Snapshot* snapshot;
 
   ReadOptions()
       : verify_checksums(false),
         fill_cache(true),
-        snapshot(NULL) {
+        snapshot(nullptr) {
   }
 };
 
diff --git a/include/leveldb/status.h b/include/leveldb/status.h
index 42ad4bb..39d692d 100644
--- a/include/leveldb/status.h
+++ b/include/leveldb/status.h
@@ -22,7 +22,7 @@ namespace leveldb {
 class LEVELDB_EXPORT Status {
  public:
   // Create a success status.
-  Status() : state_(NULL) { }
+  Status() : state_(nullptr) { }
   ~Status() { delete[] state_; }
 
   // Copy the specified status.
@@ -50,7 +50,7 @@ class LEVELDB_EXPORT Status {
   }
 
   // Returns true iff the status indicates success.
-  bool ok() const { return (state_ == NULL); }
+  bool ok() const { return (state_ == nullptr); }
 
   // Returns true iff the status indicates a NotFound error.
   bool IsNotFound() const { return code() == kNotFound; }
@@ -72,7 +72,7 @@ class LEVELDB_EXPORT Status {
   std::string ToString() const;
 
  private:
-  // OK status has a NULL state_.  Otherwise, state_ is a new[] array
+  // OK status has a null state_.  Otherwise, state_ is a new[] array
   // of the following form:
   //    state_[0..3] == length of message
   //    state_[4]    == code
@@ -89,7 +89,7 @@ class LEVELDB_EXPORT Status {
   };
 
   Code code() const {
-    return (state_ == NULL) ? kOk : static_cast<Code>(state_[4]);
+    return (state_ == nullptr) ? kOk : static_cast<Code>(state_[4]);
   }
 
   Status(Code code, const Slice& msg, const Slice& msg2);
@@ -97,14 +97,14 @@ class LEVELDB_EXPORT Status {
 };
 
 inline Status::Status(const Status& s) {
-  state_ = (s.state_ == NULL) ? NULL : CopyState(s.state_);
+  state_ = (s.state_ == nullptr) ? nullptr : CopyState(s.state_);
 }
 inline void Status::operator=(const Status& s) {
   // The following condition catches both aliasing (when this == &s),
   // and the common case where both s and *this are ok.
   if (state_ != s.state_) {
     delete[] state_;
-    state_ = (s.state_ == NULL) ? NULL : CopyState(s.state_);
+    state_ = (s.state_ == nullptr) ? nullptr : CopyState(s.state_);
   }
 }
 
diff --git a/include/leveldb/table.h b/include/leveldb/table.h
index 83078d2..e9f6641 100644
--- a/include/leveldb/table.h
+++ b/include/leveldb/table.h
@@ -31,7 +31,7 @@ class LEVELDB_EXPORT Table {
   // If successful, returns ok and sets "*table" to the newly opened
   // table.  The client should delete "*table" when no longer needed.
   // If there was an error while initializing the table, sets "*table"
-  // to NULL and returns a non-ok status.  Does not take ownership of
+  // to nullptr and returns a non-ok status.  Does not take ownership of
   // "*source", but the client must ensure that "source" remains live
   // for the duration of the returned table's lifetime.
   //
diff --git a/port/port_posix.cc b/port/port_posix.cc
index 30e8007..04095bb 100644
--- a/port/port_posix.cc
+++ b/port/port_posix.cc
@@ -18,7 +18,7 @@ static void PthreadCall(const char* label, int result) {
   }
 }
 
-Mutex::Mutex() { PthreadCall("init mutex", pthread_mutex_init(&mu_, NULL)); }
+Mutex::Mutex() { PthreadCall("init mutex", pthread_mutex_init(&mu_, nullptr)); }
 
 Mutex::~Mutex() { PthreadCall("destroy mutex", pthread_mutex_destroy(&mu_)); }
 
@@ -28,7 +28,7 @@ void Mutex::Unlock() { PthreadCall("unlock", pthread_mutex_unlock(&mu_)); }
 
 CondVar::CondVar(Mutex* mu)
     : mu_(mu) {
-    PthreadCall("init cv", pthread_cond_init(&cv_, NULL));
+    PthreadCall("init cv", pthread_cond_init(&cv_, nullptr));
 }
 
 CondVar::~CondVar() { PthreadCall("destroy cv", pthread_cond_destroy(&cv_)); }
diff --git a/table/block.cc b/table/block.cc
index 43e402c..6fdfdea 100644
--- a/table/block.cc
+++ b/table/block.cc
@@ -48,13 +48,13 @@ Block::~Block() {
 // and the length of the value in "*shared", "*non_shared", and
 // "*value_length", respectively.  Will not dereference past "limit".
 //
-// If any errors are detected, returns NULL.  Otherwise, returns a
+// If any errors are detected, returns nullptr.  Otherwise, returns a
 // pointer to the key delta (just past the three decoded values).
 static inline const char* DecodeEntry(const char* p, const char* limit,
                                       uint32_t* shared,
                                       uint32_t* non_shared,
                                       uint32_t* value_length) {
-  if (limit - p < 3) return NULL;
+  if (limit - p < 3) return nullptr;
   *shared = reinterpret_cast<const unsigned char*>(p)[0];
   *non_shared = reinterpret_cast<const unsigned char*>(p)[1];
   *value_length = reinterpret_cast<const unsigned char*>(p)[2];
@@ -62,13 +62,13 @@ static inline const char* DecodeEntry(const char* p, const char* limit,
     // Fast path: all three values are encoded in one byte each
     p += 3;
   } else {
-    if ((p = GetVarint32Ptr(p, limit, shared)) == NULL) return NULL;
-    if ((p = GetVarint32Ptr(p, limit, non_shared)) == NULL) return NULL;
-    if ((p = GetVarint32Ptr(p, limit, value_length)) == NULL) return NULL;
+    if ((p = GetVarint32Ptr(p, limit, shared)) == nullptr) return nullptr;
+    if ((p = GetVarint32Ptr(p, limit, non_shared)) == nullptr) return nullptr;
+    if ((p = GetVarint32Ptr(p, limit, value_length)) == nullptr) return nullptr;
   }
 
   if (static_cast<uint32_t>(limit - p) < (*non_shared + *value_length)) {
-    return NULL;
+    return nullptr;
   }
   return p;
 }
@@ -174,7 +174,7 @@ class Block::Iter : public Iterator {
       const char* key_ptr = DecodeEntry(data_ + region_offset,
                                         data_ + restarts_,
                                         &shared, &non_shared, &value_length);
-      if (key_ptr == NULL || (shared != 0)) {
+      if (key_ptr == nullptr || (shared != 0)) {
         CorruptionError();
         return;
       }
@@ -237,7 +237,7 @@ class Block::Iter : public Iterator {
     // Decode next entry
     uint32_t shared, non_shared, value_length;
     p = DecodeEntry(p, limit, &shared, &non_shared, &value_length);
-    if (p == NULL || key_.size() < shared) {
+    if (p == nullptr || key_.size() < shared) {
       CorruptionError();
       return false;
     } else {
diff --git a/table/filter_block.cc b/table/filter_block.cc
index 1ed5134..ce0aa04 100644
--- a/table/filter_block.cc
+++ b/table/filter_block.cc
@@ -78,8 +78,8 @@ void FilterBlockBuilder::GenerateFilter() {
 FilterBlockReader::FilterBlockReader(const FilterPolicy* policy,
                                      const Slice& contents)
     : policy_(policy),
-      data_(NULL),
-      offset_(NULL),
+      data_(nullptr),
+      offset_(nullptr),
       num_(0),
       base_lg_(0) {
   size_t n = contents.size();
diff --git a/table/iterator.cc b/table/iterator.cc
index 3d1c87f..aff0e59 100644
--- a/table/iterator.cc
+++ b/table/iterator.cc
@@ -7,14 +7,14 @@
 namespace leveldb {
 
 Iterator::Iterator() {
-  cleanup_.function = NULL;
-  cleanup_.next = NULL;
+  cleanup_.function = nullptr;
+  cleanup_.next = nullptr;
 }
 
 Iterator::~Iterator() {
-  if (cleanup_.function != NULL) {
+  if (cleanup_.function != nullptr) {
     (*cleanup_.function)(cleanup_.arg1, cleanup_.arg2);
-    for (Cleanup* c = cleanup_.next; c != NULL; ) {
+    for (Cleanup* c = cleanup_.next; c != nullptr; ) {
       (*c->function)(c->arg1, c->arg2);
       Cleanup* next = c->next;
       delete c;
@@ -24,9 +24,9 @@ Iterator::~Iterator() {
 }
 
 void Iterator::RegisterCleanup(CleanupFunction func, void* arg1, void* arg2) {
-  assert(func != NULL);
+  assert(func != nullptr);
   Cleanup* c;
-  if (cleanup_.function == NULL) {
+  if (cleanup_.function == nullptr) {
     c = &cleanup_;
   } else {
     c = new Cleanup;
diff --git a/table/iterator_wrapper.h b/table/iterator_wrapper.h
index f410c3f..f1814ca 100644
--- a/table/iterator_wrapper.h
+++ b/table/iterator_wrapper.h
@@ -16,8 +16,8 @@ namespace leveldb {
 // cache locality.
 class IteratorWrapper {
  public:
-  IteratorWrapper(): iter_(NULL), valid_(false) { }
-  explicit IteratorWrapper(Iterator* iter): iter_(NULL) {
+  IteratorWrapper(): iter_(nullptr), valid_(false) { }
+  explicit IteratorWrapper(Iterator* iter): iter_(nullptr) {
     Set(iter);
   }
   ~IteratorWrapper() { delete iter_; }
@@ -28,7 +28,7 @@ class IteratorWrapper {
   void Set(Iterator* iter) {
     delete iter_;
     iter_ = iter;
-    if (iter_ == NULL) {
+    if (iter_ == nullptr) {
       valid_ = false;
     } else {
       Update();
@@ -40,7 +40,7 @@ class IteratorWrapper {
   bool Valid() const        { return valid_; }
   Slice key() const         { assert(Valid()); return key_; }
   Slice value() const       { assert(Valid()); return iter_->value(); }
-  // Methods below require iter() != NULL
+  // Methods below require iter() != nullptr
   Status status() const     { assert(iter_); return iter_->status(); }
   void Next()               { assert(iter_); iter_->Next();        Update(); }
   void Prev()               { assert(iter_); iter_->Prev();        Update(); }
diff --git a/table/merger.cc b/table/merger.cc
index 2dde4dc..e079680 100644
--- a/table/merger.cc
+++ b/table/merger.cc
@@ -17,7 +17,7 @@ class MergingIterator : public Iterator {
       : comparator_(comparator),
         children_(new IteratorWrapper[n]),
         n_(n),
-        current_(NULL),
+        current_(nullptr),
         direction_(kForward) {
     for (int i = 0; i < n; i++) {
       children_[i].Set(children[i]);
@@ -29,7 +29,7 @@ class MergingIterator : public Iterator {
   }
 
   virtual bool Valid() const {
-    return (current_ != NULL);
+    return (current_ != nullptr);
   }
 
   virtual void SeekToFirst() {
@@ -153,11 +153,11 @@ class MergingIterator : public Iterator {
 };
 
 void MergingIterator::FindSmallest() {
-  IteratorWrapper* smallest = NULL;
+  IteratorWrapper* smallest = nullptr;
   for (int i = 0; i < n_; i++) {
     IteratorWrapper* child = &children_[i];
     if (child->Valid()) {
-      if (smallest == NULL) {
+      if (smallest == nullptr) {
         smallest = child;
       } else if (comparator_->Compare(child->key(), smallest->key()) < 0) {
         smallest = child;
@@ -168,11 +168,11 @@ void MergingIterator::FindSmallest() {
 }
 
 void MergingIterator::FindLargest() {
-  IteratorWrapper* largest = NULL;
+  IteratorWrapper* largest = nullptr;
   for (int i = n_-1; i >= 0; i--) {
     IteratorWrapper* child = &children_[i];
     if (child->Valid()) {
-      if (largest == NULL) {
+      if (largest == nullptr) {
         largest = child;
       } else if (comparator_->Compare(child->key(), largest->key()) > 0) {
         largest = child;
diff --git a/table/table.cc b/table/table.cc
index ff73cee..8e737e1 100644
--- a/table/table.cc
+++ b/table/table.cc
@@ -39,7 +39,7 @@ Status Table::Open(const Options& options,
                    RandomAccessFile* file,
                    uint64_t size,
                    Table** table) {
-  *table = NULL;
+  *table = nullptr;
   if (size < Footer::kEncodedLength) {
     return Status::Corruption("file is too short to be an sstable");
   }
@@ -74,8 +74,8 @@ Status Table::Open(const Options& options,
     rep->metaindex_handle = footer.metaindex_handle();
     rep->index_block = index_block;
     rep->cache_id = (options.block_cache ? options.block_cache->NewId() : 0);
-    rep->filter_data = NULL;
-    rep->filter = NULL;
+    rep->filter_data = nullptr;
+    rep->filter = nullptr;
     *table = new Table(rep);
     (*table)->ReadMeta(footer);
   }
@@ -84,7 +84,7 @@ Status Table::Open(const Options& options,
 }
 
 void Table::ReadMeta(const Footer& footer) {
-  if (rep_->options.filter_policy == NULL) {
+  if (rep_->options.filter_policy == nullptr) {
     return;  // Do not need any metadata
   }
 
@@ -161,8 +161,8 @@ Iterator* Table::BlockReader(void* arg,
                              const Slice& index_value) {
   Table* table = reinterpret_cast<Table*>(arg);
   Cache* block_cache = table->rep_->options.block_cache;
-  Block* block = NULL;
-  Cache::Handle* cache_handle = NULL;
+  Block* block = nullptr;
+  Cache::Handle* cache_handle = nullptr;
 
   BlockHandle handle;
   Slice input = index_value;
@@ -172,13 +172,13 @@ Iterator* Table::BlockReader(void* arg,
 
   if (s.ok()) {
     BlockContents contents;
-    if (block_cache != NULL) {
+    if (block_cache != nullptr) {
       char cache_key_buffer[16];
       EncodeFixed64(cache_key_buffer, table->rep_->cache_id);
       EncodeFixed64(cache_key_buffer+8, handle.offset());
       Slice key(cache_key_buffer, sizeof(cache_key_buffer));
       cache_handle = block_cache->Lookup(key);
-      if (cache_handle != NULL) {
+      if (cache_handle != nullptr) {
         block = reinterpret_cast<Block*>(block_cache->Value(cache_handle));
       } else {
         s = ReadBlock(table->rep_->file, options, handle, &contents);
@@ -199,10 +199,10 @@ Iterator* Table::BlockReader(void* arg,
   }
 
   Iterator* iter;
-  if (block != NULL) {
+  if (block != nullptr) {
     iter = block->NewIterator(table->rep_->options.comparator);
-    if (cache_handle == NULL) {
-      iter->RegisterCleanup(&DeleteBlock, block, NULL);
+    if (cache_handle == nullptr) {
+      iter->RegisterCleanup(&DeleteBlock, block, nullptr);
     } else {
       iter->RegisterCleanup(&ReleaseBlock, block_cache, cache_handle);
     }
@@ -228,7 +228,7 @@ Status Table::InternalGet(const ReadOptions& options, const Slice& k,
     Slice handle_value = iiter->value();
     FilterBlockReader* filter = rep_->filter;
     BlockHandle handle;
-    if (filter != NULL &&
+    if (filter != nullptr &&
         handle.DecodeFrom(&handle_value).ok() &&
         !filter->KeyMayMatch(handle.offset(), k)) {
       // Not found
diff --git a/table/table_builder.cc b/table/table_builder.cc
index 62002c8..444d4f9 100644
--- a/table/table_builder.cc
+++ b/table/table_builder.cc
@@ -53,7 +53,7 @@ struct TableBuilder::Rep {
         index_block(&index_block_options),
         num_entries(0),
         closed(false),
-        filter_block(opt.filter_policy == NULL ? NULL
+        filter_block(opt.filter_policy == nullptr ? nullptr
                      : new FilterBlockBuilder(opt.filter_policy)),
         pending_index_entry(false) {
     index_block_options.block_restart_interval = 1;
@@ -62,7 +62,7 @@ struct TableBuilder::Rep {
 
 TableBuilder::TableBuilder(const Options& options, WritableFile* file)
     : rep_(new Rep(options, file)) {
-  if (rep_->filter_block != NULL) {
+  if (rep_->filter_block != nullptr) {
     rep_->filter_block->StartBlock(0);
   }
 }
@@ -106,7 +106,7 @@ void TableBuilder::Add(const Slice& key, const Slice& value) {
     r->pending_index_entry = false;
   }
 
-  if (r->filter_block != NULL) {
+  if (r->filter_block != nullptr) {
     r->filter_block->AddKey(key);
   }
 
@@ -131,7 +131,7 @@ void TableBuilder::Flush() {
     r->pending_index_entry = true;
     r->status = r->file->Flush();
   }
-  if (r->filter_block != NULL) {
+  if (r->filter_block != nullptr) {
     r->filter_block->StartBlock(r->offset);
   }
 }
@@ -205,7 +205,7 @@ Status TableBuilder::Finish() {
   BlockHandle filter_block_handle, metaindex_block_handle, index_block_handle;
 
   // Write filter block
-  if (ok() && r->filter_block != NULL) {
+  if (ok() && r->filter_block != nullptr) {
     WriteRawBlock(r->filter_block->Finish(), kNoCompression,
                   &filter_block_handle);
   }
@@ -213,7 +213,7 @@ Status TableBuilder::Finish() {
   // Write metaindex block
   if (ok()) {
     BlockBuilder meta_index_block(&r->options);
-    if (r->filter_block != NULL) {
+    if (r->filter_block != nullptr) {
       // Add mapping from "filter.Name" to location of filter data
       std::string key = "filter.";
       key.append(r->options.filter_policy->Name());
diff --git a/table/table_test.cc b/table/table_test.cc
index abf6e24..e47db3d 100644
--- a/table/table_test.cc
+++ b/table/table_test.cc
@@ -172,7 +172,7 @@ class Constructor {
 
   virtual const KVMap& data() { return data_; }
 
-  virtual DB* db() const { return NULL; }  // Overridden in DBConstructor
+  virtual DB* db() const { return nullptr; }  // Overridden in DBConstructor
 
  private:
   KVMap data_;
@@ -183,13 +183,13 @@ class BlockConstructor: public Constructor {
   explicit BlockConstructor(const Comparator* cmp)
       : Constructor(cmp),
         comparator_(cmp),
-        block_(NULL) { }
+        block_(nullptr) { }
   ~BlockConstructor() {
     delete block_;
   }
   virtual Status FinishImpl(const Options& options, const KVMap& data) {
     delete block_;
-    block_ = NULL;
+    block_ = nullptr;
     BlockBuilder builder(&options);
 
     for (KVMap::const_iterator it = data.begin();
@@ -222,7 +222,7 @@ class TableConstructor: public Constructor {
  public:
   TableConstructor(const Comparator* cmp)
       : Constructor(cmp),
-        source_(NULL), table_(NULL) {
+        source_(nullptr), table_(nullptr) {
   }
   ~TableConstructor() {
     Reset();
@@ -262,8 +262,8 @@ class TableConstructor: public Constructor {
   void Reset() {
     delete table_;
     delete source_;
-    table_ = NULL;
-    source_ = NULL;
+    table_ = nullptr;
+    source_ = nullptr;
   }
 
   StringSource* source_;
@@ -351,7 +351,7 @@ class DBConstructor: public Constructor {
   explicit DBConstructor(const Comparator* cmp)
       : Constructor(cmp),
         comparator_(cmp) {
-    db_ = NULL;
+    db_ = nullptr;
     NewDB();
   }
   ~DBConstructor() {
@@ -359,7 +359,7 @@ class DBConstructor: public Constructor {
   }
   virtual Status FinishImpl(const Options& options, const KVMap& data) {
     delete db_;
-    db_ = NULL;
+    db_ = nullptr;
     NewDB();
     for (KVMap::const_iterator it = data.begin();
          it != data.end();
@@ -436,11 +436,11 @@ static const int kNumTestArgs = sizeof(kTestArgList) / sizeof(kTestArgList[0]);
 
 class Harness {
  public:
-  Harness() : constructor_(NULL) { }
+  Harness() : constructor_(nullptr) { }
 
   void Init(const TestArgs& args) {
     delete constructor_;
-    constructor_ = NULL;
+    constructor_ = nullptr;
     options_ = Options();
 
     options_.block_restart_interval = args.restart_interval;
@@ -636,7 +636,7 @@ class Harness {
     }
   }
 
-  // Returns NULL if not running against a DB
+  // Returns nullptr if not running against a DB
   DB* db() const { return constructor_->db(); }
 
  private:
diff --git a/table/two_level_iterator.cc b/table/two_level_iterator.cc
index 7822eba..4e6f420 100644
--- a/table/two_level_iterator.cc
+++ b/table/two_level_iterator.cc
@@ -46,7 +46,7 @@ class TwoLevelIterator: public Iterator {
     // It'd be nice if status() returned a const Status& instead of a Status
     if (!index_iter_.status().ok()) {
       return index_iter_.status();
-    } else if (data_iter_.iter() != NULL && !data_iter_.status().ok()) {
+    } else if (data_iter_.iter() != nullptr && !data_iter_.status().ok()) {
       return data_iter_.status();
     } else {
       return status_;
@@ -67,8 +67,8 @@ class TwoLevelIterator: public Iterator {
   const ReadOptions options_;
   Status status_;
   IteratorWrapper index_iter_;
-  IteratorWrapper data_iter_; // May be NULL
-  // If data_iter_ is non-NULL, then "data_block_handle_" holds the
+  IteratorWrapper data_iter_; // May be nullptr
+  // If data_iter_ is non-null, then "data_block_handle_" holds the
   // "index_value" passed to block_function_ to create the data_iter_.
   std::string data_block_handle_;
 };
@@ -82,7 +82,7 @@ TwoLevelIterator::TwoLevelIterator(
       arg_(arg),
       options_(options),
       index_iter_(index_iter),
-      data_iter_(NULL) {
+      data_iter_(nullptr) {
 }
 
 TwoLevelIterator::~TwoLevelIterator() {
@@ -91,21 +91,21 @@ TwoLevelIterator::~TwoLevelIterator() {
 void TwoLevelIterator::Seek(const Slice& target) {
   index_iter_.Seek(target);
   InitDataBlock();
-  if (data_iter_.iter() != NULL) data_iter_.Seek(target);
+  if (data_iter_.iter() != nullptr) data_iter_.Seek(target);
   SkipEmptyDataBlocksForward();
 }
 
 void TwoLevelIterator::SeekToFirst() {
   index_iter_.SeekToFirst();
   InitDataBlock();
-  if (data_iter_.iter() != NULL) data_iter_.SeekToFirst();
+  if (data_iter_.iter() != nullptr) data_iter_.SeekToFirst();
   SkipEmptyDataBlocksForward();
 }
 
 void TwoLevelIterator::SeekToLast() {
   index_iter_.SeekToLast();
   InitDataBlock();
-  if (data_iter_.iter() != NULL) data_iter_.SeekToLast();
+  if (data_iter_.iter() != nullptr) data_iter_.SeekToLast();
   SkipEmptyDataBlocksBackward();
 }
 
@@ -123,42 +123,42 @@ void TwoLevelIterator::Prev() {
 
 
 void TwoLevelIterator::SkipEmptyDataBlocksForward() {
-  while (data_iter_.iter() == NULL || !data_iter_.Valid()) {
+  while (data_iter_.iter() == nullptr || !data_iter_.Valid()) {
     // Move to next block
     if (!index_iter_.Valid()) {
-      SetDataIterator(NULL);
+      SetDataIterator(nullptr);
       return;
     }
     index_iter_.Next();
     InitDataBlock();
-    if (data_iter_.iter() != NULL) data_iter_.SeekToFirst();
+    if (data_iter_.iter() != nullptr) data_iter_.SeekToFirst();
   }
 }
 
 void TwoLevelIterator::SkipEmptyDataBlocksBackward() {
-  while (data_iter_.iter() == NULL || !data_iter_.Valid()) {
+  while (data_iter_.iter() == nullptr || !data_iter_.Valid()) {
     // Move to next block
     if (!index_iter_.Valid()) {
-      SetDataIterator(NULL);
+      SetDataIterator(nullptr);
       return;
     }
     index_iter_.Prev();
     InitDataBlock();
-    if (data_iter_.iter() != NULL) data_iter_.SeekToLast();
+    if (data_iter_.iter() != nullptr) data_iter_.SeekToLast();
   }
 }
 
 void TwoLevelIterator::SetDataIterator(Iterator* data_iter) {
-  if (data_iter_.iter() != NULL) SaveError(data_iter_.status());
+  if (data_iter_.iter() != nullptr) SaveError(data_iter_.status());
   data_iter_.Set(data_iter);
 }
 
 void TwoLevelIterator::InitDataBlock() {
   if (!index_iter_.Valid()) {
-    SetDataIterator(NULL);
+    SetDataIterator(nullptr);
   } else {
     Slice handle = index_iter_.value();
-    if (data_iter_.iter() != NULL && handle.compare(data_block_handle_) == 0) {
+    if (data_iter_.iter() != nullptr && handle.compare(data_block_handle_) == 0) {
       // data_iter_ is already constructed with this iterator, so
       // no need to change anything
     } else {
diff --git a/util/arena.cc b/util/arena.cc
index 7407821..a0338bf 100644
--- a/util/arena.cc
+++ b/util/arena.cc
@@ -10,7 +10,7 @@ namespace leveldb {
 static const int kBlockSize = 4096;
 
 Arena::Arena() : memory_usage_(0) {
-  alloc_ptr_ = NULL;  // First allocation will allocate a block
+  alloc_ptr_ = nullptr;  // First allocation will allocate a block
   alloc_bytes_remaining_ = 0;
 }
 
diff --git a/util/cache.cc b/util/cache.cc
index 10b7103..7cc2cea 100644
--- a/util/cache.cc
+++ b/util/cache.cc
@@ -69,7 +69,7 @@ struct LRUHandle {
 // 4.4.3's builtin hashtable.
 class HandleTable {
  public:
-  HandleTable() : length_(0), elems_(0), list_(NULL) { Resize(); }
+  HandleTable() : length_(0), elems_(0), list_(nullptr) { Resize(); }
   ~HandleTable() { delete[] list_; }
 
   LRUHandle* Lookup(const Slice& key, uint32_t hash) {
@@ -79,9 +79,9 @@ class HandleTable {
   LRUHandle* Insert(LRUHandle* h) {
     LRUHandle** ptr = FindPointer(h->key(), h->hash);
     LRUHandle* old = *ptr;
-    h->next_hash = (old == NULL ? NULL : old->next_hash);
+    h->next_hash = (old == nullptr ? nullptr : old->next_hash);
     *ptr = h;
-    if (old == NULL) {
+    if (old == nullptr) {
       ++elems_;
       if (elems_ > length_) {
         // Since each cache entry is fairly large, we aim for a small
@@ -95,7 +95,7 @@ class HandleTable {
   LRUHandle* Remove(const Slice& key, uint32_t hash) {
     LRUHandle** ptr = FindPointer(key, hash);
     LRUHandle* result = *ptr;
-    if (result != NULL) {
+    if (result != nullptr) {
       *ptr = result->next_hash;
       --elems_;
     }
@@ -114,7 +114,7 @@ class HandleTable {
   // pointer to the trailing slot in the corresponding linked list.
   LRUHandle** FindPointer(const Slice& key, uint32_t hash) {
     LRUHandle** ptr = &list_[hash & (length_ - 1)];
-    while (*ptr != NULL &&
+    while (*ptr != nullptr &&
            ((*ptr)->hash != hash || key != (*ptr)->key())) {
       ptr = &(*ptr)->next_hash;
     }
@@ -131,7 +131,7 @@ class HandleTable {
     uint32_t count = 0;
     for (uint32_t i = 0; i < length_; i++) {
       LRUHandle* h = list_[i];
-      while (h != NULL) {
+      while (h != nullptr) {
         LRUHandle* next = h->next_hash;
         uint32_t hash = h->hash;
         LRUHandle** ptr = &new_list[hash & (new_length - 1)];
@@ -255,7 +255,7 @@ void LRUCache::LRU_Append(LRUHandle* list, LRUHandle* e) {
 Cache::Handle* LRUCache::Lookup(const Slice& key, uint32_t hash) {
   MutexLock l(&mutex_);
   LRUHandle* e = table_.Lookup(key, hash);
-  if (e != NULL) {
+  if (e != nullptr) {
     Ref(e);
   }
   return reinterpret_cast<Cache::Handle*>(e);
@@ -290,7 +290,7 @@ Cache::Handle* LRUCache::Insert(
     FinishErase(table_.Insert(e));
   } else {  // don't cache. (capacity_==0 is supported and turns off caching.)
     // next is read by key() in an assert, so it must be initialized
-    e->next = NULL;
+    e->next = nullptr;
   }
   while (usage_ > capacity_ && lru_.next != &lru_) {
     LRUHandle* old = lru_.next;
@@ -304,17 +304,17 @@ Cache::Handle* LRUCache::Insert(
   return reinterpret_cast<Cache::Handle*>(e);
 }
 
-// If e != NULL, finish removing *e from the cache; it has already been removed
-// from the hash table.  Return whether e != NULL.  Requires mutex_ held.
+// If e != nullptr, finish removing *e from the cache; it has already been
+// removed from the hash table.  Return whether e != nullptr.
 bool LRUCache::FinishErase(LRUHandle* e) {
-  if (e != NULL) {
+  if (e != nullptr) {
     assert(e->in_cache);
     LRU_Remove(e);
     e->in_cache = false;
     usage_ -= e->charge;
     Unref(e);
   }
-  return e != NULL;
+  return e != nullptr;
 }
 
 void LRUCache::Erase(const Slice& key, uint32_t hash) {
diff --git a/util/cache_test.cc b/util/cache_test.cc
index 246ab8e..8647feb 100644
--- a/util/cache_test.cc
+++ b/util/cache_test.cc
@@ -47,8 +47,8 @@ class CacheTest {
 
   int Lookup(int key) {
     Cache::Handle* handle = cache_->Lookup(EncodeKey(key));
-    const int r = (handle == NULL) ? -1 : DecodeValue(cache_->Value(handle));
-    if (handle != NULL) {
+    const int r = (handle == nullptr) ? -1 : DecodeValue(cache_->Value(handle));
+    if (handle != nullptr) {
       cache_->Release(handle);
     }
     return r;
diff --git a/util/coding.cc b/util/coding.cc
index 21e3186..9e72613 100644
--- a/util/coding.cc
+++ b/util/coding.cc
@@ -125,14 +125,14 @@ const char* GetVarint32PtrFallback(const char* p,
       return reinterpret_cast<const char*>(p);
     }
   }
-  return NULL;
+  return nullptr;
 }
 
 bool GetVarint32(Slice* input, uint32_t* value) {
   const char* p = input->data();
   const char* limit = p + input->size();
   const char* q = GetVarint32Ptr(p, limit, value);
-  if (q == NULL) {
+  if (q == nullptr) {
     return false;
   } else {
     *input = Slice(q, limit - q);
@@ -154,14 +154,14 @@ const char* GetVarint64Ptr(const char* p, const char* limit, uint64_t* value) {
       return reinterpret_cast<const char*>(p);
     }
   }
-  return NULL;
+  return nullptr;
 }
 
 bool GetVarint64(Slice* input, uint64_t* value) {
   const char* p = input->data();
   const char* limit = p + input->size();
   const char* q = GetVarint64Ptr(p, limit, value);
-  if (q == NULL) {
+  if (q == nullptr) {
     return false;
   } else {
     *input = Slice(q, limit - q);
@@ -173,8 +173,8 @@ const char* GetLengthPrefixedSlice(const char* p, const char* limit,
                                    Slice* result) {
   uint32_t len;
   p = GetVarint32Ptr(p, limit, &len);
-  if (p == NULL) return NULL;
-  if (p + len > limit) return NULL;
+  if (p == nullptr) return nullptr;
+  if (p + len > limit) return nullptr;
   *result = Slice(p, len);
   return p + len;
 }
diff --git a/util/coding.h b/util/coding.h
index 1fb3d66..f0fa2cb 100644
--- a/util/coding.h
+++ b/util/coding.h
@@ -35,7 +35,7 @@ bool GetLengthPrefixedSlice(Slice* input, Slice* result);
 
 // Pointer-based variants of GetVarint...  These either store a value
 // in *v and return a pointer just past the parsed value, or return
-// NULL on error.  These routines only look at bytes in the range
+// nullptr on error.  These routines only look at bytes in the range
 // [p..limit-1]
 const char* GetVarint32Ptr(const char* p, const char* limit, uint32_t* v);
 const char* GetVarint64Ptr(const char* p, const char* limit, uint64_t* v);
diff --git a/util/coding_test.cc b/util/coding_test.cc
index 22f6adc..d315e19 100644
--- a/util/coding_test.cc
+++ b/util/coding_test.cc
@@ -89,7 +89,7 @@ TEST(Coding, Varint32) {
     uint32_t actual;
     const char* start = p;
     p = GetVarint32Ptr(p, limit, &actual);
-    ASSERT_TRUE(p != NULL);
+    ASSERT_TRUE(p != nullptr);
     ASSERT_EQ(expected, actual);
     ASSERT_EQ(VarintLength(actual), p - start);
   }
@@ -124,19 +124,18 @@ TEST(Coding, Varint64) {
     uint64_t actual;
     const char* start = p;
     p = GetVarint64Ptr(p, limit, &actual);
-    ASSERT_TRUE(p != NULL);
+    ASSERT_TRUE(p != nullptr);
     ASSERT_EQ(values[i], actual);
     ASSERT_EQ(VarintLength(actual), p - start);
   }
   ASSERT_EQ(p, limit);
-
 }
 
 TEST(Coding, Varint32Overflow) {
   uint32_t result;
   std::string input("\x81\x82\x83\x84\x85\x11");
   ASSERT_TRUE(GetVarint32Ptr(input.data(), input.data() + input.size(), &result)
-              == NULL);
+              == nullptr);
 }
 
 TEST(Coding, Varint32Truncation) {
@@ -145,9 +144,10 @@ TEST(Coding, Varint32Truncation) {
   PutVarint32(&s, large_value);
   uint32_t result;
   for (size_t len = 0; len < s.size() - 1; len++) {
-    ASSERT_TRUE(GetVarint32Ptr(s.data(), s.data() + len, &result) == NULL);
+    ASSERT_TRUE(GetVarint32Ptr(s.data(), s.data() + len, &result) == nullptr);
   }
-  ASSERT_TRUE(GetVarint32Ptr(s.data(), s.data() + s.size(), &result) != NULL);
+  ASSERT_TRUE(
+      GetVarint32Ptr(s.data(), s.data() + s.size(), &result) != nullptr);
   ASSERT_EQ(large_value, result);
 }
 
@@ -155,7 +155,7 @@ TEST(Coding, Varint64Overflow) {
   uint64_t result;
   std::string input("\x81\x82\x83\x84\x85\x81\x82\x83\x84\x85\x11");
   ASSERT_TRUE(GetVarint64Ptr(input.data(), input.data() + input.size(), &result)
-              == NULL);
+              == nullptr);
 }
 
 TEST(Coding, Varint64Truncation) {
@@ -164,9 +164,10 @@ TEST(Coding, Varint64Truncation) {
   PutVarint64(&s, large_value);
   uint64_t result;
   for (size_t len = 0; len < s.size() - 1; len++) {
-    ASSERT_TRUE(GetVarint64Ptr(s.data(), s.data() + len, &result) == NULL);
+    ASSERT_TRUE(GetVarint64Ptr(s.data(), s.data() + len, &result) == nullptr);
   }
-  ASSERT_TRUE(GetVarint64Ptr(s.data(), s.data() + s.size(), &result) != NULL);
+  ASSERT_TRUE(
+      GetVarint64Ptr(s.data(), s.data() + s.size(), &result) != nullptr);
   ASSERT_EQ(large_value, result);
 }
 
diff --git a/util/env.cc b/util/env.cc
index c58a082..40a1363 100644
--- a/util/env.cc
+++ b/util/env.cc
@@ -29,7 +29,7 @@ FileLock::~FileLock() {
 }
 
 void Log(Logger* info_log, const char* format, ...) {
-  if (info_log != NULL) {
+  if (info_log != nullptr) {
     va_list ap;
     va_start(ap, format);
     info_log->Logv(format, ap);
diff --git a/util/env_posix.cc b/util/env_posix.cc
index 4bfaf6c..e758d5f 100644
--- a/util/env_posix.cc
+++ b/util/env_posix.cc
@@ -282,7 +282,7 @@ class PosixWritableFile : public WritableFile {
     const char* sep = strrchr(f, '/');
     Slice basename;
     std::string dir;
-    if (sep == NULL) {
+    if (sep == nullptr) {
       dir = ".";
       basename = f;
     } else {
@@ -390,7 +390,7 @@ class PosixEnv : public Env {
                                    SequentialFile** result) {
     int fd = open(fname.c_str(), O_RDONLY);
     if (fd < 0) {
-      *result = NULL;
+      *result = nullptr;
       return PosixError(fname, errno);
     } else {
       *result = new PosixSequentialFile(fname, fd);
@@ -400,7 +400,7 @@ class PosixEnv : public Env {
 
   virtual Status NewRandomAccessFile(const std::string& fname,
                                      RandomAccessFile** result) {
-    *result = NULL;
+    *result = nullptr;
     Status s;
     int fd = open(fname.c_str(), O_RDONLY);
     if (fd < 0) {
@@ -409,7 +409,7 @@ class PosixEnv : public Env {
       uint64_t size;
       s = GetFileSize(fname, &size);
       if (s.ok()) {
-        void* base = mmap(NULL, size, PROT_READ, MAP_SHARED, fd, 0);
+        void* base = mmap(nullptr, size, PROT_READ, MAP_SHARED, fd, 0);
         if (base != MAP_FAILED) {
           *result = new PosixMmapReadableFile(fname, base, size, &mmap_limit_);
         } else {
@@ -431,7 +431,7 @@ class PosixEnv : public Env {
     Status s;
     int fd = open(fname.c_str(), O_TRUNC | O_WRONLY | O_CREAT, 0644);
     if (fd < 0) {
-      *result = NULL;
+      *result = nullptr;
       s = PosixError(fname, errno);
     } else {
       *result = new PosixWritableFile(fname, fd);
@@ -444,7 +444,7 @@ class PosixEnv : public Env {
     Status s;
     int fd = open(fname.c_str(), O_APPEND | O_WRONLY | O_CREAT, 0644);
     if (fd < 0) {
-      *result = NULL;
+      *result = nullptr;
       s = PosixError(fname, errno);
     } else {
       *result = new PosixWritableFile(fname, fd);
@@ -460,11 +460,11 @@ class PosixEnv : public Env {
                              std::vector<std::string>* result) {
     result->clear();
     DIR* d = opendir(dir.c_str());
-    if (d == NULL) {
+    if (d == nullptr) {
       return PosixError(dir, errno);
     }
     struct dirent* entry;
-    while ((entry = readdir(d)) != NULL) {
+    while ((entry = readdir(d)) != nullptr) {
       result->push_back(entry->d_name);
     }
     closedir(d);
@@ -516,7 +516,7 @@ class PosixEnv : public Env {
   }
 
   virtual Status LockFile(const std::string& fname, FileLock** lock) {
-    *lock = NULL;
+    *lock = nullptr;
     Status result;
     int fd = open(fname.c_str(), O_RDWR | O_CREAT, 0644);
     if (fd < 0) {
@@ -576,8 +576,8 @@ class PosixEnv : public Env {
 
   virtual Status NewLogger(const std::string& fname, Logger** result) {
     FILE* f = fopen(fname.c_str(), "w");
-    if (f == NULL) {
-      *result = NULL;
+    if (f == nullptr) {
+      *result = nullptr;
       return PosixError(fname, errno);
     } else {
       *result = new PosixLogger(f, &PosixEnv::gettid);
@@ -587,7 +587,7 @@ class PosixEnv : public Env {
 
   virtual uint64_t NowMicros() {
     struct timeval tv;
-    gettimeofday(&tv, NULL);
+    gettimeofday(&tv, nullptr);
     return static_cast<uint64_t>(tv.tv_sec) * 1000000 + tv.tv_usec;
   }
 
@@ -607,7 +607,7 @@ class PosixEnv : public Env {
   void BGThread();
   static void* BGThreadWrapper(void* arg) {
     reinterpret_cast<PosixEnv*>(arg)->BGThread();
-    return NULL;
+    return nullptr;
   }
 
   pthread_mutex_t mu_;
@@ -657,8 +657,8 @@ PosixEnv::PosixEnv()
     : started_bgthread_(false),
       mmap_limit_(MaxMmaps()),
       fd_limit_(MaxOpenFiles()) {
-  PthreadCall("mutex_init", pthread_mutex_init(&mu_, NULL));
-  PthreadCall("cvar_init", pthread_cond_init(&bgsignal_, NULL));
+  PthreadCall("mutex_init", pthread_mutex_init(&mu_, nullptr));
+  PthreadCall("cvar_init", pthread_cond_init(&bgsignal_, nullptr));
 }
 
 void PosixEnv::Schedule(void (*function)(void*), void* arg) {
@@ -669,7 +669,7 @@ void PosixEnv::Schedule(void (*function)(void*), void* arg) {
     started_bgthread_ = true;
     PthreadCall(
         "create thread",
-        pthread_create(&bgthread_, NULL,  &PosixEnv::BGThreadWrapper, this));
+        pthread_create(&bgthread_, nullptr,  &PosixEnv::BGThreadWrapper, this));
   }
 
   // If the queue is currently empty, the background thread may currently be
@@ -713,7 +713,7 @@ static void* StartThreadWrapper(void* arg) {
   StartThreadState* state = reinterpret_cast<StartThreadState*>(arg);
   state->user_function(state->arg);
   delete state;
-  return NULL;
+  return nullptr;
 }
 
 void PosixEnv::StartThread(void (*function)(void* arg), void* arg) {
@@ -722,7 +722,7 @@ void PosixEnv::StartThread(void (*function)(void* arg), void* arg) {
   state->user_function = function;
   state->arg = arg;
   PthreadCall("start thread",
-              pthread_create(&t, NULL,  &StartThreadWrapper, state));
+              pthread_create(&t, nullptr,  &StartThreadWrapper, state));
 }
 
 }  // namespace
@@ -732,12 +732,12 @@ static Env* default_env;
 static void InitDefaultEnv() { default_env = new PosixEnv; }
 
 void EnvPosixTestHelper::SetReadOnlyFDLimit(int limit) {
-  assert(default_env == NULL);
+  assert(default_env == nullptr);
   open_read_only_file_limit = limit;
 }
 
 void EnvPosixTestHelper::SetReadOnlyMMapLimit(int limit) {
-  assert(default_env == NULL);
+  assert(default_env == nullptr);
   mmap_limit = limit;
 }
 
diff --git a/util/env_posix_test.cc b/util/env_posix_test.cc
index 295f8ae..e28df9a 100644
--- a/util/env_posix_test.cc
+++ b/util/env_posix_test.cc
@@ -32,7 +32,7 @@ TEST(EnvPosixTest, TestOpenOnRead) {
   std::string test_file = test_dir + "/open_on_read.txt";
 
   FILE* f = fopen(test_file.c_str(), "w");
-  ASSERT_TRUE(f != NULL);
+  ASSERT_TRUE(f != nullptr);
   const char kFileData[] = "abcdefghijklmnopqrstuvwxyz";
   fputs(kFileData, f);
   fclose(f);
diff --git a/util/env_test.cc b/util/env_test.cc
index fd89b4c..070109b 100644
--- a/util/env_test.cc
+++ b/util/env_test.cc
@@ -77,14 +77,14 @@ TEST(EnvTest, ReadWrite) {
 }
 
 TEST(EnvTest, RunImmediately) {
-  port::AtomicPointer called (NULL);
+  port::AtomicPointer called(nullptr);
   env_->Schedule(&SetBool, &called);
   env_->SleepForMicroseconds(kDelayMicros);
-  ASSERT_TRUE(called.NoBarrier_Load() != NULL);
+  ASSERT_TRUE(called.NoBarrier_Load() != nullptr);
 }
 
 TEST(EnvTest, RunMany) {
-  port::AtomicPointer last_id (NULL);
+  port::AtomicPointer last_id(nullptr);
 
   struct CB {
     port::AtomicPointer* last_id_ptr;   // Pointer to shared slot
diff --git a/util/options.cc b/util/options.cc
index b5e6227..351fa39 100644
--- a/util/options.cc
+++ b/util/options.cc
@@ -15,16 +15,16 @@ Options::Options()
       error_if_exists(false),
       paranoid_checks(false),
       env(Env::Default()),
-      info_log(NULL),
+      info_log(nullptr),
       write_buffer_size(4<<20),
       max_open_files(1000),
-      block_cache(NULL),
+      block_cache(nullptr),
       block_size(4096),
       block_restart_interval(16),
       max_file_size(2<<20),
       compression(kSnappyCompression),
       reuse_logs(false),
-      filter_policy(NULL) {
+      filter_policy(nullptr) {
 }
 
 }  // namespace leveldb
diff --git a/util/posix_logger.h b/util/posix_logger.h
index 9741b1a..1909e61 100644
--- a/util/posix_logger.h
+++ b/util/posix_logger.h
@@ -45,7 +45,7 @@ class PosixLogger : public Logger {
       char* limit = base + bufsize;
 
       struct timeval now_tv;
-      gettimeofday(&now_tv, NULL);
+      gettimeofday(&now_tv, nullptr);
       const time_t seconds = now_tv.tv_sec;
       struct tm t;
       localtime_r(&seconds, &t);
diff --git a/util/status.cc b/util/status.cc
index a44f35b..5591381 100644
--- a/util/status.cc
+++ b/util/status.cc
@@ -34,7 +34,7 @@ Status::Status(Code code, const Slice& msg, const Slice& msg2) {
 }
 
 std::string Status::ToString() const {
-  if (state_ == NULL) {
+  if (state_ == nullptr) {
     return "OK";
   } else {
     char tmp[30];
diff --git a/util/testharness.cc b/util/testharness.cc
index 95f025f..37ba410 100644
--- a/util/testharness.cc
+++ b/util/testharness.cc
@@ -26,7 +26,7 @@ std::vector<Test>* tests;
 }
 
 bool RegisterTest(const char* base, const char* name, void (*func)()) {
-  if (tests == NULL) {
+  if (tests == nullptr) {
     tests = new std::vector<Test>;
   }
   Test t;
@@ -41,14 +41,14 @@ int RunAllTests() {
   const char* matcher = getenv("LEVELDB_TESTS");
 
   int num = 0;
-  if (tests != NULL) {
+  if (tests != nullptr) {
     for (size_t i = 0; i < tests->size(); i++) {
       const Test& t = (*tests)[i];
-      if (matcher != NULL) {
+      if (matcher != nullptr) {
         std::string name = t.base;
         name.push_back('.');
         name.append(t.name);
-        if (strstr(name.c_str(), matcher) == NULL) {
+        if (strstr(name.c_str(), matcher) == nullptr) {
           continue;
         }
       }
@@ -70,7 +70,7 @@ std::string TmpDir() {
 
 int RandomSeed() {
   const char* env = getenv("TEST_RANDOM_SEED");
-  int result = (env != NULL ? atoi(env) : 301);
+  int result = (env != nullptr ? atoi(env) : 301);
   if (result <= 0) {
     result = 301;
   }
diff --git a/util/testutil.h b/util/testutil.h
index 8726bf7..dc77ac3 100644
--- a/util/testutil.h
+++ b/util/testutil.h
@@ -40,7 +40,7 @@ class ErrorEnv : public EnvWrapper {
                                  WritableFile** result) {
     if (writable_file_error_) {
       ++num_writable_file_errors_;
-      *result = NULL;
+      *result = nullptr;
       return Status::IOError(fname, "fake error");
     }
     return target()->NewWritableFile(fname, result);
@@ -50,7 +50,7 @@ class ErrorEnv : public EnvWrapper {
                                    WritableFile** result) {
     if (writable_file_error_) {
       ++num_writable_file_errors_;
-      *result = NULL;
+      *result = nullptr;
       return Status::IOError(fname, "fake error");
     }
     return target()->NewAppendableFile(fname, result);