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
22 #include <string>
23
24 #include "leveldb/export.h"
25
26 namespace leveldb {
27
28 class LEVELDB_EXPORT Slice {
29 public:
30 // Create an empty slice.
Slice()31 Slice() : data_(""), size_(0) {}
32
33 // Create a slice that refers to d[0,n-1].
Slice(const char * d,size_t n)34 Slice(const char* d, size_t n) : data_(d), size_(n) {}
35
36 // Create a slice that refers to the contents of "s"
Slice(const std::string & s)37 Slice(const std::string& s) : data_(s.data()), size_(s.size()) {}
38
39 // Create a slice that refers to s[0,strlen(s)-1]
Slice(const char * s)40 Slice(const char* s) : data_(s), size_(strlen(s)) {}
41
42 // Intentionally copyable.
43 Slice(const Slice&) = default;
44 Slice& operator=(const Slice&) = default;
45
46 // Return a pointer to the beginning of the referenced data
data()47 const char* data() const { return data_; }
48
49 // Return the length (in bytes) of the referenced data
size()50 size_t size() const { return size_; }
51
52 // Return true iff the length of the referenced data is zero
empty()53 bool empty() const { return size_ == 0; }
54
55 // Return the ith byte in the referenced data.
56 // REQUIRES: n < size()
57 char operator[](size_t n) const {
58 assert(n < size());
59 return data_[n];
60 }
61
62 // Change this slice to refer to an empty array
clear()63 void clear() {
64 data_ = "";
65 size_ = 0;
66 }
67
68 // Drop the first "n" bytes from this slice.
remove_prefix(size_t n)69 void remove_prefix(size_t n) {
70 assert(n <= size());
71 data_ += n;
72 size_ -= n;
73 }
74
75 // Return a string that contains the copy of the referenced data.
ToString()76 std::string ToString() const { return std::string(data_, size_); }
77
78 // Three-way comparison. Returns value:
79 // < 0 iff "*this" < "b",
80 // == 0 iff "*this" == "b",
81 // > 0 iff "*this" > "b"
82 int compare(const Slice& b) const;
83
84 // Return true iff "x" is a prefix of "*this"
starts_with(const Slice & x)85 bool starts_with(const Slice& x) const {
86 return ((size_ >= x.size_) && (memcmp(data_, x.data_, x.size_) == 0));
87 }
88
89 private:
90 const char* data_;
91 size_t size_;
92 };
93
94 inline bool operator==(const Slice& x, const Slice& y) {
95 return ((x.size() == y.size()) &&
96 (memcmp(x.data(), y.data(), x.size()) == 0));
97 }
98
99 inline bool operator!=(const Slice& x, const Slice& y) { return !(x == y); }
100
compare(const Slice & b)101 inline int Slice::compare(const Slice& b) const {
102 const size_t min_len = (size_ < b.size_) ? size_ : b.size_;
103 int r = memcmp(data_, b.data_, min_len);
104 if (r == 0) {
105 if (size_ < b.size_)
106 r = -1;
107 else if (size_ > b.size_)
108 r = +1;
109 }
110 return r;
111 }
112
113 } // namespace leveldb
114
115 #endif // STORAGE_LEVELDB_INCLUDE_SLICE_H_
116