1 // Copyright (c) 2006-2008 The Chromium Authors. All rights reserved. 2 // 3 // Redistribution and use in source and binary forms, with or without 4 // modification, are permitted provided that the following conditions are 5 // met: 6 // 7 // * Redistributions of source code must retain the above copyright 8 // notice, this list of conditions and the following disclaimer. 9 // * Redistributions in binary form must reproduce the above 10 // copyright notice, this list of conditions and the following disclaimer 11 // in the documentation and/or other materials provided with the 12 // distribution. 13 // * Neither the name of Google Inc. nor the names of its 14 // contributors may be used to endorse or promote products derived from 15 // this software without specific prior written permission. 16 // 17 // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS 18 // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT 19 // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR 20 // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT 21 // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, 22 // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT 23 // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, 24 // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY 25 // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT 26 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE 27 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 28 29 #ifndef BASE_STRING16_H_ 30 #define BASE_STRING16_H_ 31 32 // WHAT: 33 // A version of std::basic_string that provides 2-byte characters even when 34 // wchar_t is not implemented as a 2-byte type. You can access this class as 35 // string16. We also define char16, which string16 is based upon. 36 // 37 // WHY: 38 // On Windows, wchar_t is 2 bytes, and it can conveniently handle UTF-16/UCS-2 39 // data. Plenty of existing code operates on strings encoded as UTF-16. 40 // 41 // On many other platforms, sizeof(wchar_t) is 4 bytes by default. We can make 42 // it 2 bytes by using the GCC flag -fshort-wchar. But then std::wstring fails 43 // at run time, because it calls some functions (like wcslen) that come from 44 // the system's native C library -- which was built with a 4-byte wchar_t! 45 // It's wasteful to use 4-byte wchar_t strings to carry UTF-16 data, and it's 46 // entirely improper on those systems where the encoding of wchar_t is defined 47 // as UTF-32. 48 // 49 // Here, we define string16, which is similar to std::wstring but replaces all 50 // libc functions with custom, 2-byte-char compatible routines. It is capable 51 // of carrying UTF-16-encoded data. 52 53 #include <string> 54 55 #include "base/basictypes.h" 56 57 #ifdef WIN32 58 59 typedef wchar_t char16; 60 typedef std::wstring string16; 61 62 #else // !WIN32 63 64 typedef uint16 char16; 65 66 namespace base { 67 68 // char16 versions of the functions required by string16_char_traits; these 69 // are based on the wide character functions of similar names ("w" or "wcs" 70 // instead of "c16"). 71 int c16memcmp(const char16* s1, const char16* s2, size_t n); 72 size_t c16len(const char16* s); 73 const char16* c16memchr(const char16* s, char16 c, size_t n); 74 char16* c16memmove(char16* s1, const char16* s2, size_t n); 75 char16* c16memcpy(char16* s1, const char16* s2, size_t n); 76 char16* c16memset(char16* s, char16 c, size_t n); 77 78 struct string16_char_traits { 79 typedef char16 char_type; 80 typedef int int_type; 81 82 typedef std::streamoff off_type; 83 typedef mbstate_t state_type; 84 typedef std::fpos<state_type> pos_type; 85 86 static void assign(char_type& c1, const char_type& c2) { 87 c1 = c2; 88 } 89 90 static bool eq(const char_type& c1, const char_type& c2) { 91 return c1 == c2; 92 } 93 static bool lt(const char_type& c1, const char_type& c2) { 94 return c1 < c2; 95 } 96 97 static int compare(const char_type* s1, const char_type* s2, size_t n) { 98 return c16memcmp(s1, s2, n); 99 } 100 101 static size_t length(const char_type* s) { 102 return c16len(s); 103 } 104 105 static const char_type* find(const char_type* s, size_t n, 106 const char_type& a) { 107 return c16memchr(s, a, n); 108 } 109 110 static char_type* move(char_type* s1, const char_type* s2, int_type n) { 111 return c16memmove(s1, s2, n); 112 } 113 114 static char_type* copy(char_type* s1, const char_type* s2, size_t n) { 115 return c16memcpy(s1, s2, n); 116 } 117 118 static char_type* assign(char_type* s, size_t n, char_type a) { 119 return c16memset(s, a, n); 120 } 121 122 static int_type not_eof(const int_type& c) { 123 return eq_int_type(c, eof()) ? 0 : c; 124 } 125 126 static char_type to_char_type(const int_type& c) { 127 return char_type(c); 128 } 129 130 static int_type to_int_type(const char_type& c) { 131 return int_type(c); 132 } 133 134 static bool eq_int_type(const int_type& c1, const int_type& c2) { 135 return c1 == c2; 136 } 137 138 static int_type eof() { 139 return static_cast<int_type>(EOF); 140 } 141 }; 142 143 } // namespace base 144 145 // The string class will be explicitly instantiated only once, in string16.cc. 146 // 147 // std::basic_string<> in GNU libstdc++ contains a static data member, 148 // _S_empty_rep_storage, to represent empty strings. When an operation such 149 // as assignment or destruction is performed on a string, causing its existing 150 // data member to be invalidated, it must not be freed if this static data 151 // member is being used. Otherwise, it counts as an attempt to free static 152 // (and not allocated) data, which is a memory error. 153 // 154 // Generally, due to C++ template magic, _S_empty_rep_storage will be marked 155 // as a coalesced symbol, meaning that the linker will combine multiple 156 // instances into a single one when generating output. 157 // 158 // If a string class is used by multiple shared libraries, a problem occurs. 159 // Each library will get its own copy of _S_empty_rep_storage. When strings 160 // are passed across a library boundary for alteration or destruction, memory 161 // errors will result. GNU libstdc++ contains a configuration option, 162 // --enable-fully-dynamic-string (_GLIBCXX_FULLY_DYNAMIC_STRING), which 163 // disables the static data member optimization, but it's a good optimization 164 // and non-STL code is generally at the mercy of the system's STL 165 // configuration. Fully-dynamic strings are not the default for GNU libstdc++ 166 // libstdc++ itself or for the libstdc++ installations on the systems we care 167 // about, such as Mac OS X and relevant flavors of Linux. 168 // 169 // See also http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24196 . 170 // 171 // To avoid problems, string classes need to be explicitly instantiated only 172 // once, in exactly one library. All other string users see it via an "extern" 173 // declaration. This is precisely how GNU libstdc++ handles 174 // std::basic_string<char> (string) and std::basic_string<wchar_t> (wstring). 175 // 176 // This also works around a Mac OS X linker bug in ld64-85.2.1 (Xcode 3.1.2), 177 // in which the linker does not fully coalesce symbols when dead code 178 // stripping is enabled. This bug causes the memory errors described above 179 // to occur even when a std::basic_string<> does not cross shared library 180 // boundaries, such as in statically-linked executables. 181 // 182 // TODO(mark): File this bug with Apple and update this note with a bug number. 183 184 extern template class std::basic_string<char16, base::string16_char_traits>; 185 186 typedef std::basic_string<char16, base::string16_char_traits> string16; 187 188 extern std::ostream& operator<<(std::ostream& out, const string16& str); 189 190 #endif // !WIN32 191 192 #endif // BASE_STRING16_H_ 193
