小组成员:10215300402-朱维清 & 10222140408 谷杰

114 lignes
3.2 KiB

  1. // Copyright (c) 2011 The LevelDB Authors. All rights reserved.
  2. // Use of this source code is governed by a BSD-style license that can be
  3. // found in the LICENSE file. See the AUTHORS file for names of contributors.
  4. //
  5. // Slice is a simple structure containing a pointer into some external
  6. // storage and a size. The user of a Slice must ensure that the slice
  7. // is not used after the corresponding external storage has been
  8. // deallocated.
  9. //
  10. // Multiple threads can invoke const methods on a Slice without
  11. // external synchronization, but if any of the threads may call a
  12. // non-const method, all threads accessing the same Slice must use
  13. // external synchronization.
  14. #ifndef STORAGE_LEVELDB_INCLUDE_SLICE_H_
  15. #define STORAGE_LEVELDB_INCLUDE_SLICE_H_
  16. #include <cassert>
  17. #include <cstddef>
  18. #include <cstring>
  19. #include <string>
  20. #include "leveldb/export.h"
  21. namespace leveldb {
  22. class LEVELDB_EXPORT Slice {
  23. public:
  24. // Create an empty slice.
  25. Slice() : data_(""), size_(0) {}
  26. // Create a slice that refers to d[0,n-1].
  27. Slice(const char* d, size_t n) : data_(d), size_(n) {}
  28. // Create a slice that refers to the contents of "s"
  29. Slice(const std::string& s) : data_(s.data()), size_(s.size()) {}
  30. // Create a slice that refers to s[0,strlen(s)-1]
  31. Slice(const char* s) : data_(s), size_(strlen(s)) {}
  32. // Intentionally copyable.
  33. Slice(const Slice&) = default;
  34. Slice& operator=(const Slice&) = default;
  35. // Return a pointer to the beginning of the referenced data
  36. const char* data() const { return data_; }
  37. // Return the length (in bytes) of the referenced data
  38. size_t size() const { return size_; }
  39. // Return true iff the length of the referenced data is zero
  40. bool empty() const { return size_ == 0; }
  41. // Return the ith byte in the referenced data.
  42. // REQUIRES: n < size()
  43. char operator[](size_t n) const {
  44. assert(n < size());
  45. return data_[n];
  46. }
  47. // Change this slice to refer to an empty array
  48. void clear() {
  49. data_ = "";
  50. size_ = 0;
  51. }
  52. // Drop the first "n" bytes from this slice.
  53. void remove_prefix(size_t n) {
  54. assert(n <= size());
  55. data_ += n;
  56. size_ -= n;
  57. }
  58. // Return a string that contains the copy of the referenced data.
  59. std::string ToString() const { return std::string(data_, size_); }
  60. // Three-way comparison. Returns value:
  61. // < 0 iff "*this" < "b",
  62. // == 0 iff "*this" == "b",
  63. // > 0 iff "*this" > "b"
  64. int compare(const Slice& b) const;
  65. // Return true iff "x" is a prefix of "*this"
  66. bool starts_with(const Slice& x) const {
  67. return ((size_ >= x.size_) && (memcmp(data_, x.data_, x.size_) == 0));
  68. }
  69. private:
  70. const char* data_;
  71. size_t size_;
  72. };
  73. inline bool operator==(const Slice& x, const Slice& y) {
  74. return ((x.size() == y.size()) &&
  75. (memcmp(x.data(), y.data(), x.size()) == 0));
  76. }
  77. inline bool operator!=(const Slice& x, const Slice& y) { return !(x == y); }
  78. inline int Slice::compare(const Slice& b) const {
  79. const size_t min_len = (size_ < b.size_) ? size_ : b.size_;
  80. int r = memcmp(data_, b.data_, min_len);
  81. if (r == 0) {
  82. if (size_ < b.size_)
  83. r = -1;
  84. else if (size_ > b.size_)
  85. r = +1;
  86. }
  87. return r;
  88. }
  89. } // namespace leveldb
  90. #endif // STORAGE_LEVELDB_INCLUDE_SLICE_H_