| // Copyright 2013 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_STRINGS_STRING16_H_ |
| #define BASE_STRINGS_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" |
| #include "build/build_config.h" |
| |
| #if defined(WCHAR_T_IS_UTF16) |
| |
| namespace url { |
| namespace base { |
| |
| typedef wchar_t char16; |
| typedef std::wstring string16; |
| typedef std::char_traits<wchar_t> string16_char_traits; |
| |
| } // namespace base |
| } // namespace url |
| |
| #elif defined(WCHAR_T_IS_UTF32) |
| |
| namespace url { |
| namespace base { |
| |
| typedef uint16 char16; |
| |
| // 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); |
| } |
| }; |
| |
| typedef std::basic_string<char16, url::base::string16_char_traits> string16; |
| |
| } // namespace base |
| } // namespace url |
| |
| // 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<url::base::char16, url::base::string16_char_traits>; |
| |
| #endif // WCHAR_T_IS_UTF32 |
| |
| #endif // BASE_STRINGS_STRING16_H_ |