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 15 #ifndef STORAGE_LEVELDB_INCLUDE_SLICE_H_ 16 #define STORAGE_LEVELDB_INCLUDE_SLICE_H_ 17 18 #include <assert.h> 19 #include <stddef.h> 20 #include <string.h> 21 #include <string> 22 23 namespace leveldb { 24 25 class Slice { 26 public: 27 // Create an empty slice. 28 Slice() : data_(""), size_(0) { } 29 30 // Create a slice that refers to d[0,n-1]. 31 Slice(const char* d, size_t n) : data_(d), size_(n) { } 32 33 // Create a slice that refers to the contents of "s" 34 Slice(const std::string& s) : data_(s.data()), size_(s.size()) { } 35 36 // Create a slice that refers to s[0,strlen(s)-1] 37 Slice(const char* s) : data_(s), size_(strlen(s)) { } 38 39 // Return a pointer to the beginning of the referenced data 40 const char* data() const { return data_; } 41 42 // Return the length (in bytes) of the referenced data 43 size_t size() const { return size_; } 44 45 // Return true iff the length of the referenced data is zero 46 bool empty() const { return size_ == 0; } 47 48 // Return the ith byte in the referenced data. 49 // REQUIRES: n < size() 50 char operator[](size_t n) const { 51 assert(n < size()); 52 return data_[n]; 53 } 54 55 // Change this slice to refer to an empty array 56 void clear() { data_ = ""; size_ = 0; } 57 58 // Drop the first "n" bytes from this slice. 59 void remove_prefix(size_t n) { 60 assert(n <= size()); 61 data_ += n; 62 size_ -= n; 63 } 64 65 // Return a string that contains the copy of the referenced data. 66 std::string ToString() const { return std::string(data_, size_); } 67 68 // Three-way comparison. Returns value: 69 // < 0 iff "*this" < "b", 70 // == 0 iff "*this" == "b", 71 // > 0 iff "*this" > "b" 72 int compare(const Slice& b) const; 73 74 // Return true iff "x" is a prefix of "*this" 75 bool starts_with(const Slice& x) const { 76 return ((size_ >= x.size_) && 77 (memcmp(data_, x.data_, x.size_) == 0)); 78 } 79 80 private: 81 const char* data_; 82 size_t size_; 83 84 // Intentionally copyable 85 }; 86 87 inline bool operator==(const Slice& x, const Slice& y) { 88 return ((x.size() == y.size()) && 89 (memcmp(x.data(), y.data(), x.size()) == 0)); 90 } 91 92 inline bool operator!=(const Slice& x, const Slice& y) { 93 return !(x == y); 94 } 95 96 inline int Slice::compare(const Slice& b) const { 97 const int min_len = (size_ < b.size_) ? size_ : b.size_; 98 int r = memcmp(data_, b.data_, min_len); 99 if (r == 0) { 100 if (size_ < b.size_) r = -1; 101 else if (size_ > b.size_) r = +1; 102 } 103 return r; 104 } 105 106 } // namespace leveldb 107 108 109 #endif // STORAGE_LEVELDB_INCLUDE_SLICE_H_ 110
