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