1 : // Copyright (c) 2006-2008 The Chromium 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.
4 :
5 : #ifndef BASE_STRING16_H_
6 : #define BASE_STRING16_H_
7 :
8 : // WHAT:
9 : // A version of std::basic_string that provides 2-byte characters even when
10 : // wchar_t is not implemented as a 2-byte type. You can access this class as
11 : // string16. We also define char16, which string16 is based upon.
12 : //
13 : // WHY:
14 : // On Windows, wchar_t is 2 bytes, and it can conveniently handle UTF-16/UCS-2
15 : // data. Plenty of existing code operates on strings encoded as UTF-16.
16 : //
17 : // On many other platforms, sizeof(wchar_t) is 4 bytes by default. We can make
18 : // it 2 bytes by using the GCC flag -fshort-wchar. But then std::wstring fails
19 : // at run time, because it calls some functions (like wcslen) that come from
20 : // the system's native C library -- which was built with a 4-byte wchar_t!
21 : // It's wasteful to use 4-byte wchar_t strings to carry UTF-16 data, and it's
22 : // entirely improper on those systems where the encoding of wchar_t is defined
23 : // as UTF-32.
24 : //
25 : // Here, we define string16, which is similar to std::wstring but replaces all
26 : // libc functions with custom, 2-byte-char compatible routines. It is capable
27 : // of carrying UTF-16-encoded data.
28 :
29 : #include <stdio.h>
30 : #include <string>
31 :
32 : #include "base/basictypes.h"
33 :
34 : #if defined(WCHAR_T_IS_UTF16)
35 :
36 : typedef wchar_t char16;
37 : typedef std::wstring string16;
38 :
39 : #elif defined(WCHAR_T_IS_UTF32)
40 :
41 : typedef uint16 char16;
42 :
43 : namespace base {
44 :
45 : // char16 versions of the functions required by string16_char_traits; these
46 : // are based on the wide character functions of similar names ("w" or "wcs"
47 : // instead of "c16").
48 : int c16memcmp(const char16* s1, const char16* s2, size_t n);
49 : size_t c16len(const char16* s);
50 : const char16* c16memchr(const char16* s, char16 c, size_t n);
51 : char16* c16memmove(char16* s1, const char16* s2, size_t n);
52 : char16* c16memcpy(char16* s1, const char16* s2, size_t n);
53 : char16* c16memset(char16* s, char16 c, size_t n);
54 :
55 : struct string16_char_traits {
56 : typedef char16 char_type;
57 : typedef int int_type;
58 :
59 : // int_type needs to be able to hold each possible value of char_type, and in
60 : // addition, the distinct value of eof().
61 : COMPILE_ASSERT(sizeof(int_type) > sizeof(char_type), unexpected_type_width);
62 :
63 : typedef std::streamoff off_type;
64 : typedef mbstate_t state_type;
65 : typedef std::fpos<state_type> pos_type;
66 :
67 0 : static void assign(char_type& c1, const char_type& c2) {
68 0 : c1 = c2;
69 0 : }
70 :
71 0 : static bool eq(const char_type& c1, const char_type& c2) {
72 0 : return c1 == c2;
73 : }
74 : static bool lt(const char_type& c1, const char_type& c2) {
75 : return c1 < c2;
76 : }
77 :
78 0 : static int compare(const char_type* s1, const char_type* s2, size_t n) {
79 0 : return c16memcmp(s1, s2, n);
80 : }
81 :
82 0 : static size_t length(const char_type* s) {
83 0 : return c16len(s);
84 : }
85 :
86 0 : static const char_type* find(const char_type* s, size_t n,
87 : const char_type& a) {
88 0 : return c16memchr(s, a, n);
89 : }
90 :
91 0 : static char_type* move(char_type* s1, const char_type* s2, int_type n) {
92 0 : return c16memmove(s1, s2, n);
93 : }
94 :
95 0 : static char_type* copy(char_type* s1, const char_type* s2, size_t n) {
96 0 : return c16memcpy(s1, s2, n);
97 : }
98 :
99 0 : static char_type* assign(char_type* s, size_t n, char_type a) {
100 0 : return c16memset(s, a, n);
101 : }
102 :
103 : static int_type not_eof(const int_type& c) {
104 : return eq_int_type(c, eof()) ? 0 : c;
105 : }
106 :
107 : static char_type to_char_type(const int_type& c) {
108 : return char_type(c);
109 : }
110 :
111 : static int_type to_int_type(const char_type& c) {
112 : return int_type(c);
113 : }
114 :
115 : static bool eq_int_type(const int_type& c1, const int_type& c2) {
116 : return c1 == c2;
117 : }
118 :
119 : static int_type eof() {
120 : return static_cast<int_type>(EOF);
121 : }
122 : };
123 :
124 : } // namespace base
125 :
126 : // The string class will be explicitly instantiated only once, in string16.cc.
127 : //
128 : // std::basic_string<> in GNU libstdc++ contains a static data member,
129 : // _S_empty_rep_storage, to represent empty strings. When an operation such
130 : // as assignment or destruction is performed on a string, causing its existing
131 : // data member to be invalidated, it must not be freed if this static data
132 : // member is being used. Otherwise, it counts as an attempt to free static
133 : // (and not allocated) data, which is a memory error.
134 : //
135 : // Generally, due to C++ template magic, _S_empty_rep_storage will be marked
136 : // as a coalesced symbol, meaning that the linker will combine multiple
137 : // instances into a single one when generating output.
138 : //
139 : // If a string class is used by multiple shared libraries, a problem occurs.
140 : // Each library will get its own copy of _S_empty_rep_storage. When strings
141 : // are passed across a library boundary for alteration or destruction, memory
142 : // errors will result. GNU libstdc++ contains a configuration option,
143 : // --enable-fully-dynamic-string (_GLIBCXX_FULLY_DYNAMIC_STRING), which
144 : // disables the static data member optimization, but it's a good optimization
145 : // and non-STL code is generally at the mercy of the system's STL
146 : // configuration. Fully-dynamic strings are not the default for GNU libstdc++
147 : // libstdc++ itself or for the libstdc++ installations on the systems we care
148 : // about, such as Mac OS X and relevant flavors of Linux.
149 : //
150 : // See also http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24196 .
151 : //
152 : // To avoid problems, string classes need to be explicitly instantiated only
153 : // once, in exactly one library. All other string users see it via an "extern"
154 : // declaration. This is precisely how GNU libstdc++ handles
155 : // std::basic_string<char> (string) and std::basic_string<wchar_t> (wstring).
156 : //
157 : // This also works around a Mac OS X linker bug in ld64-85.2.1 (Xcode 3.1.2),
158 : // in which the linker does not fully coalesce symbols when dead code
159 : // stripping is enabled. This bug causes the memory errors described above
160 : // to occur even when a std::basic_string<> does not cross shared library
161 : // boundaries, such as in statically-linked executables.
162 : //
163 : // TODO(mark): File this bug with Apple and update this note with a bug number.
164 :
165 : extern template class std::basic_string<char16, base::string16_char_traits>;
166 :
167 : typedef std::basic_string<char16, base::string16_char_traits> string16;
168 :
169 : extern std::ostream& operator<<(std::ostream& out, const string16& str);
170 :
171 : #endif // WCHAR_T_IS_UTF32
172 :
173 : #endif // BASE_STRING16_H_
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