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#pragma once 8 9// WHAT: 10// A version of std::basic_string that provides 2-byte characters even when 11// wchar_t is not implemented as a 2-byte type. You can access this class as 12// string16. We also define char16, which string16 is based upon. 13// 14// WHY: 15// On Windows, wchar_t is 2 bytes, and it can conveniently handle UTF-16/UCS-2 16// data. Plenty of existing code operates on strings encoded as UTF-16. 17// 18// On many other platforms, sizeof(wchar_t) is 4 bytes by default. We can make 19// it 2 bytes by using the GCC flag -fshort-wchar. But then std::wstring fails 20// at run time, because it calls some functions (like wcslen) that come from 21// the system's native C library -- which was built with a 4-byte wchar_t! 22// It's wasteful to use 4-byte wchar_t strings to carry UTF-16 data, and it's 23// entirely improper on those systems where the encoding of wchar_t is defined 24// as UTF-32. 25// 26// Here, we define string16, which is similar to std::wstring but replaces all 27// libc functions with custom, 2-byte-char compatible routines. It is capable 28// of carrying UTF-16-encoded data. 29 30#include <stdio.h> 31#include <string> 32 33#include "base/base_api.h" 34#include "base/basictypes.h" 35 36#if defined(WCHAR_T_IS_UTF16) 37 38typedef wchar_t char16; 39typedef std::wstring string16; 40 41#elif defined(WCHAR_T_IS_UTF32) 42 43typedef uint16 char16; 44 45namespace base { 46 47// char16 versions of the functions required by string16_char_traits; these 48// are based on the wide character functions of similar names ("w" or "wcs" 49// instead of "c16"). 50BASE_API int c16memcmp(const char16* s1, const char16* s2, size_t n); 51BASE_API size_t c16len(const char16* s); 52BASE_API const char16* c16memchr(const char16* s, char16 c, size_t n); 53BASE_API char16* c16memmove(char16* s1, const char16* s2, size_t n); 54BASE_API char16* c16memcpy(char16* s1, const char16* s2, size_t n); 55BASE_API char16* c16memset(char16* s, char16 c, size_t n); 56 57struct 58#ifdef ANDROID 59BASE_API 60#endif 61string16_char_traits { 62 typedef char16 char_type; 63 typedef int int_type; 64 65 // int_type needs to be able to hold each possible value of char_type, and in 66 // addition, the distinct value of eof(). 67 COMPILE_ASSERT(sizeof(int_type) > sizeof(char_type), unexpected_type_width); 68 69 typedef std::streamoff off_type; 70 typedef mbstate_t state_type; 71 typedef std::fpos<state_type> pos_type; 72 73 static void assign(char_type& c1, const char_type& c2) { 74 c1 = c2; 75 } 76 77 static bool eq(const char_type& c1, const char_type& c2) { 78 return c1 == c2; 79 } 80 static bool lt(const char_type& c1, const char_type& c2) { 81 return c1 < c2; 82 } 83 84 static int compare(const char_type* s1, const char_type* s2, size_t n) { 85 return c16memcmp(s1, s2, n); 86 } 87 88 static size_t length(const char_type* s) { 89 return c16len(s); 90 } 91 92 static const char_type* find(const char_type* s, size_t n, 93 const char_type& a) { 94 return c16memchr(s, a, n); 95 } 96 97 static char_type* move(char_type* s1, const char_type* s2, int_type n) { 98 return c16memmove(s1, s2, n); 99 } 100 101 static char_type* copy(char_type* s1, const char_type* s2, size_t n) { 102 return c16memcpy(s1, s2, n); 103 } 104 105 static char_type* assign(char_type* s, size_t n, char_type a) { 106 return c16memset(s, a, n); 107 } 108 109 static int_type not_eof(const int_type& c) { 110 return eq_int_type(c, eof()) ? 0 : c; 111 } 112 113 static char_type to_char_type(const int_type& c) { 114 return char_type(c); 115 } 116 117 static int_type to_int_type(const char_type& c) { 118 return int_type(c); 119 } 120 121 static bool eq_int_type(const int_type& c1, const int_type& c2) { 122 return c1 == c2; 123 } 124 125 static int_type eof() { 126 return static_cast<int_type>(EOF); 127 } 128}; 129 130} // namespace base 131 132// The string class will be explicitly instantiated only once, in string16.cc. 133// 134// std::basic_string<> in GNU libstdc++ contains a static data member, 135// _S_empty_rep_storage, to represent empty strings. When an operation such 136// as assignment or destruction is performed on a string, causing its existing 137// data member to be invalidated, it must not be freed if this static data 138// member is being used. Otherwise, it counts as an attempt to free static 139// (and not allocated) data, which is a memory error. 140// 141// Generally, due to C++ template magic, _S_empty_rep_storage will be marked 142// as a coalesced symbol, meaning that the linker will combine multiple 143// instances into a single one when generating output. 144// 145// If a string class is used by multiple shared libraries, a problem occurs. 146// Each library will get its own copy of _S_empty_rep_storage. When strings 147// are passed across a library boundary for alteration or destruction, memory 148// errors will result. GNU libstdc++ contains a configuration option, 149// --enable-fully-dynamic-string (_GLIBCXX_FULLY_DYNAMIC_STRING), which 150// disables the static data member optimization, but it's a good optimization 151// and non-STL code is generally at the mercy of the system's STL 152// configuration. Fully-dynamic strings are not the default for GNU libstdc++ 153// libstdc++ itself or for the libstdc++ installations on the systems we care 154// about, such as Mac OS X and relevant flavors of Linux. 155// 156// See also http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24196 . 157// 158// To avoid problems, string classes need to be explicitly instantiated only 159// once, in exactly one library. All other string users see it via an "extern" 160// declaration. This is precisely how GNU libstdc++ handles 161// std::basic_string<char> (string) and std::basic_string<wchar_t> (wstring). 162// 163// This also works around a Mac OS X linker bug in ld64-85.2.1 (Xcode 3.1.2), 164// in which the linker does not fully coalesce symbols when dead code 165// stripping is enabled. This bug causes the memory errors described above 166// to occur even when a std::basic_string<> does not cross shared library 167// boundaries, such as in statically-linked executables. 168// 169// TODO(mark): File this bug with Apple and update this note with a bug number. 170 171extern template class 172#ifdef ANDROID 173BASE_API 174#endif 175std::basic_string<char16, base::string16_char_traits>; 176 177typedef std::basic_string<char16, base::string16_char_traits> string16; 178 179namespace base { 180BASE_API extern std::ostream& operator<<(std::ostream& out, const string16& str); 181} 182 183#endif // WCHAR_T_IS_UTF32 184 185#endif // BASE_STRING16_H_ 186