109 righe
3.1 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 <assert.h>
  17. #include <stddef.h>
  18. #include <string.h>
  19. #include <string>
  20. namespace leveldb {
  21. class Slice {
  22. public:
  23. // Create an empty slice.
  24. Slice() : data_(""), size_(0) { }
  25. // Create a slice that refers to d[0,n-1].
  26. Slice(const char* d, size_t n) : data_(d), size_(n) { }
  27. // Create a slice that refers to the contents of "s"
  28. Slice(const std::string& s) : data_(s.data()), size_(s.size()) { }
  29. // Create a slice that refers to s[0,strlen(s)-1]
  30. Slice(const char* s) : data_(s), size_(strlen(s)) { }
  31. // Return a pointer to the beginning of the referenced data
  32. const char* data() const { return data_; }
  33. // Return the length (in bytes) of the referenced data
  34. size_t size() const { return size_; }
  35. // Return true iff the length of the referenced data is zero
  36. bool empty() const { return size_ == 0; }
  37. // Return the ith byte in the referenced data.
  38. // REQUIRES: n < size()
  39. char operator[](size_t n) const {
  40. assert(n < size());
  41. return data_[n];
  42. }
  43. // Change this slice to refer to an empty array
  44. void clear() { data_ = ""; size_ = 0; }
  45. // Drop the first "n" bytes from this slice.
  46. void remove_prefix(size_t n) {
  47. assert(n <= size());
  48. data_ += n;
  49. size_ -= n;
  50. }
  51. // Return a string that contains the copy of the referenced data.
  52. std::string ToString() const { return std::string(data_, size_); }
  53. // Three-way comparison. Returns value:
  54. // < 0 iff "*this" < "b",
  55. // == 0 iff "*this" == "b",
  56. // > 0 iff "*this" > "b"
  57. int compare(const Slice& b) const;
  58. // Return true iff "x" is a prefix of "*this"
  59. bool starts_with(const Slice& x) const {
  60. return ((size_ >= x.size_) &&
  61. (memcmp(data_, x.data_, x.size_) == 0));
  62. }
  63. private:
  64. const char* data_;
  65. size_t size_;
  66. // Intentionally copyable
  67. };
  68. inline bool operator==(const Slice& x, const Slice& y) {
  69. return ((x.size() == y.size()) &&
  70. (memcmp(x.data(), y.data(), x.size()) == 0));
  71. }
  72. inline bool operator!=(const Slice& x, const Slice& y) {
  73. return !(x == y);
  74. }
  75. inline int Slice::compare(const Slice& b) const {
  76. const int min_len = (size_ < b.size_) ? size_ : b.size_;
  77. int r = memcmp(data_, b.data_, min_len);
  78. if (r == 0) {
  79. if (size_ < b.size_) r = -1;
  80. else if (size_ > b.size_) r = +1;
  81. }
  82. return r;
  83. }
  84. } // namespace leveldb
  85. #endif // STORAGE_LEVELDB_INCLUDE_SLICE_H_