1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
|
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
// Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef BASE_STRING16_H_
#define BASE_STRING16_H_
// WHAT:
// A version of std::basic_string that provides 2-byte characters even when
// wchar_t is not implemented as a 2-byte type. You can access this class as
// string16. We also define char16, which string16 is based upon.
//
// WHY:
// On Windows, wchar_t is 2 bytes, and it can conveniently handle UTF-16/UCS-2
// data. Plenty of existing code operates on strings encoded as UTF-16.
//
// On many other platforms, sizeof(wchar_t) is 4 bytes by default. We can make
// it 2 bytes by using the GCC flag -fshort-wchar. But then std::wstring fails
// at run time, because it calls some functions (like wcslen) that come from
// the system's native C library -- which was built with a 4-byte wchar_t!
// It's wasteful to use 4-byte wchar_t strings to carry UTF-16 data, and it's
// entirely improper on those systems where the encoding of wchar_t is defined
// as UTF-32.
//
// Here, we define string16, which is similar to std::wstring but replaces all
// libc functions with custom, 2-byte-char compatible routines. It is capable
// of carrying UTF-16-encoded data.
#include <stdio.h>
#include <string>
#include "base/basictypes.h"
#if defined(XP_WIN)
typedef wchar_t char16;
typedef std::wstring string16;
#else
typedef uint16_t char16;
namespace base {
// char16 versions of the functions required by string16_char_traits; these
// are based on the wide character functions of similar names ("w" or "wcs"
// instead of "c16").
int c16memcmp(const char16* s1, const char16* s2, size_t n);
size_t c16len(const char16* s);
const char16* c16memchr(const char16* s, char16 c, size_t n);
char16* c16memmove(char16* s1, const char16* s2, size_t n);
char16* c16memcpy(char16* s1, const char16* s2, size_t n);
char16* c16memset(char16* s, char16 c, size_t n);
struct string16_char_traits {
typedef char16 char_type;
typedef int int_type;
// int_type needs to be able to hold each possible value of char_type, and in
// addition, the distinct value of eof().
COMPILE_ASSERT(sizeof(int_type) > sizeof(char_type), unexpected_type_width);
typedef std::streamoff off_type;
typedef mbstate_t state_type;
typedef std::fpos<state_type> pos_type;
static void assign(char_type& c1, const char_type& c2) { c1 = c2; }
static bool eq(const char_type& c1, const char_type& c2) { return c1 == c2; }
static bool lt(const char_type& c1, const char_type& c2) { return c1 < c2; }
static int compare(const char_type* s1, const char_type* s2, size_t n) {
return c16memcmp(s1, s2, n);
}
static size_t length(const char_type* s) { return c16len(s); }
static const char_type* find(const char_type* s, size_t n,
const char_type& a) {
return c16memchr(s, a, n);
}
static char_type* move(char_type* s1, const char_type* s2, int_type n) {
return c16memmove(s1, s2, n);
}
static char_type* copy(char_type* s1, const char_type* s2, size_t n) {
return c16memcpy(s1, s2, n);
}
static char_type* assign(char_type* s, size_t n, char_type a) {
return c16memset(s, a, n);
}
static int_type not_eof(const int_type& c) {
return eq_int_type(c, eof()) ? 0 : c;
}
static char_type to_char_type(const int_type& c) { return char_type(c); }
static int_type to_int_type(const char_type& c) { return int_type(c); }
static bool eq_int_type(const int_type& c1, const int_type& c2) {
return c1 == c2;
}
static int_type eof() { return static_cast<int_type>(EOF); }
};
} // namespace base
// The string class will be explicitly instantiated only once, in string16.cc.
//
// std::basic_string<> in GNU libstdc++ contains a static data member,
// _S_empty_rep_storage, to represent empty strings. When an operation such
// as assignment or destruction is performed on a string, causing its existing
// data member to be invalidated, it must not be freed if this static data
// member is being used. Otherwise, it counts as an attempt to free static
// (and not allocated) data, which is a memory error.
//
// Generally, due to C++ template magic, _S_empty_rep_storage will be marked
// as a coalesced symbol, meaning that the linker will combine multiple
// instances into a single one when generating output.
//
// If a string class is used by multiple shared libraries, a problem occurs.
// Each library will get its own copy of _S_empty_rep_storage. When strings
// are passed across a library boundary for alteration or destruction, memory
// errors will result. GNU libstdc++ contains a configuration option,
// --enable-fully-dynamic-string (_GLIBCXX_FULLY_DYNAMIC_STRING), which
// disables the static data member optimization, but it's a good optimization
// and non-STL code is generally at the mercy of the system's STL
// configuration. Fully-dynamic strings are not the default for GNU libstdc++
// libstdc++ itself or for the libstdc++ installations on the systems we care
// about, such as Mac OS X and relevant flavors of Linux.
//
// See also http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24196 .
//
// To avoid problems, string classes need to be explicitly instantiated only
// once, in exactly one library. All other string users see it via an "extern"
// declaration. This is precisely how GNU libstdc++ handles
// std::basic_string<char> (string) and std::basic_string<wchar_t> (wstring).
//
// This also works around a Mac OS X linker bug in ld64-85.2.1 (Xcode 3.1.2),
// in which the linker does not fully coalesce symbols when dead code
// stripping is enabled. This bug causes the memory errors described above
// to occur even when a std::basic_string<> does not cross shared library
// boundaries, such as in statically-linked executables.
//
// TODO(mark): File this bug with Apple and update this note with a bug number.
extern template class std::basic_string<char16, base::string16_char_traits>;
typedef std::basic_string<char16, base::string16_char_traits> string16;
extern std::ostream& operator<<(std::ostream& out, const string16& str);
#endif
#endif // BASE_STRING16_H_
|
