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.
Slice()28 Slice() : data_(""), size_(0) { }
29
30 // Create a slice that refers to d[0,n-1].
Slice(const char * d,size_t n)31 Slice(const char* d, size_t n) : data_(d), size_(n) { }
32
33 // Create a slice that refers to the contents of "s"
Slice(const std::string & 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]
Slice(const char * s)37 Slice(const char* s) : data_(s), size_(strlen(s)) { }
38
39 // Return a pointer to the beginning of the referenced data
data()40 const char* data() const { return data_; }
41
42 // Return the length (in bytes) of the referenced data
size()43 size_t size() const { return size_; }
44
45 // Return true iff the length of the referenced data is zero
empty()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
clear()56 void clear() { data_ = ""; size_ = 0; }
57
58 // Drop the first "n" bytes from this slice.
remove_prefix(size_t n)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.
ToString()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"
starts_with(const Slice & x)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
compare(const Slice & b)96 inline int Slice::compare(const Slice& b) const {
97 const size_t 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