michael@0: // Copyright (c) 2006-2008 The Chromium Authors. All rights reserved.
michael@0: // Use of this source code is governed by a BSD-style license that can be
michael@0: // found in the LICENSE file.
michael@0: 
michael@0: #ifndef BASE_STRING16_H_
michael@0: #define BASE_STRING16_H_
michael@0: 
michael@0: // WHAT:
michael@0: // A version of std::basic_string that provides 2-byte characters even when
michael@0: // wchar_t is not implemented as a 2-byte type. You can access this class as
michael@0: // string16. We also define char16, which string16 is based upon.
michael@0: //
michael@0: // WHY:
michael@0: // On Windows, wchar_t is 2 bytes, and it can conveniently handle UTF-16/UCS-2
michael@0: // data. Plenty of existing code operates on strings encoded as UTF-16.
michael@0: //
michael@0: // On many other platforms, sizeof(wchar_t) is 4 bytes by default. We can make
michael@0: // it 2 bytes by using the GCC flag -fshort-wchar. But then std::wstring fails
michael@0: // at run time, because it calls some functions (like wcslen) that come from
michael@0: // the system's native C library -- which was built with a 4-byte wchar_t!
michael@0: // It's wasteful to use 4-byte wchar_t strings to carry UTF-16 data, and it's
michael@0: // entirely improper on those systems where the encoding of wchar_t is defined
michael@0: // as UTF-32.
michael@0: //
michael@0: // Here, we define string16, which is similar to std::wstring but replaces all
michael@0: // libc functions with custom, 2-byte-char compatible routines. It is capable
michael@0: // of carrying UTF-16-encoded data.
michael@0: 
michael@0: #include <stdio.h>
michael@0: #include <string>
michael@0: 
michael@0: #include "base/basictypes.h"
michael@0: 
michael@0: #if defined(WCHAR_T_IS_UTF16)
michael@0: 
michael@0: typedef wchar_t char16;
michael@0: typedef std::wstring string16;
michael@0: 
michael@0: #elif defined(WCHAR_T_IS_UTF32)
michael@0: 
michael@0: typedef uint16_t char16;
michael@0: 
michael@0: namespace base {
michael@0: 
michael@0: // char16 versions of the functions required by string16_char_traits; these
michael@0: // are based on the wide character functions of similar names ("w" or "wcs"
michael@0: // instead of "c16").
michael@0: int c16memcmp(const char16* s1, const char16* s2, size_t n);
michael@0: size_t c16len(const char16* s);
michael@0: const char16* c16memchr(const char16* s, char16 c, size_t n);
michael@0: char16* c16memmove(char16* s1, const char16* s2, size_t n);
michael@0: char16* c16memcpy(char16* s1, const char16* s2, size_t n);
michael@0: char16* c16memset(char16* s, char16 c, size_t n);
michael@0: 
michael@0: struct string16_char_traits {
michael@0:   typedef char16 char_type;
michael@0:   typedef int int_type;
michael@0: 
michael@0:   // int_type needs to be able to hold each possible value of char_type, and in
michael@0:   // addition, the distinct value of eof().
michael@0:   COMPILE_ASSERT(sizeof(int_type) > sizeof(char_type), unexpected_type_width);
michael@0: 
michael@0:   typedef std::streamoff off_type;
michael@0:   typedef mbstate_t state_type;
michael@0:   typedef std::fpos<state_type> pos_type;
michael@0: 
michael@0:   static void assign(char_type& c1, const char_type& c2) {
michael@0:     c1 = c2;
michael@0:   }
michael@0: 
michael@0:   static bool eq(const char_type& c1, const char_type& c2) {
michael@0:     return c1 == c2;
michael@0:   }
michael@0:   static bool lt(const char_type& c1, const char_type& c2) {
michael@0:     return c1 < c2;
michael@0:   }
michael@0: 
michael@0:   static int compare(const char_type* s1, const char_type* s2, size_t n) {
michael@0:     return c16memcmp(s1, s2, n);
michael@0:   }
michael@0: 
michael@0:   static size_t length(const char_type* s) {
michael@0:     return c16len(s);
michael@0:   }
michael@0: 
michael@0:   static const char_type* find(const char_type* s, size_t n,
michael@0:                                const char_type& a) {
michael@0:     return c16memchr(s, a, n);
michael@0:   }
michael@0: 
michael@0:   static char_type* move(char_type* s1, const char_type* s2, int_type n) {
michael@0:     return c16memmove(s1, s2, n);
michael@0:   }
michael@0: 
michael@0:   static char_type* copy(char_type* s1, const char_type* s2, size_t n) {
michael@0:     return c16memcpy(s1, s2, n);
michael@0:   }
michael@0: 
michael@0:   static char_type* assign(char_type* s, size_t n, char_type a) {
michael@0:     return c16memset(s, a, n);
michael@0:   }
michael@0: 
michael@0:   static int_type not_eof(const int_type& c) {
michael@0:     return eq_int_type(c, eof()) ? 0 : c;
michael@0:   }
michael@0: 
michael@0:   static char_type to_char_type(const int_type& c) {
michael@0:     return char_type(c);
michael@0:   }
michael@0: 
michael@0:   static int_type to_int_type(const char_type& c) {
michael@0:     return int_type(c);
michael@0:   }
michael@0: 
michael@0:   static bool eq_int_type(const int_type& c1, const int_type& c2) {
michael@0:     return c1 == c2;
michael@0:   }
michael@0: 
michael@0:   static int_type eof() {
michael@0:     return static_cast<int_type>(EOF);
michael@0:   }
michael@0: };
michael@0: 
michael@0: }  // namespace base
michael@0: 
michael@0: // The string class will be explicitly instantiated only once, in string16.cc.
michael@0: //
michael@0: // std::basic_string<> in GNU libstdc++ contains a static data member,
michael@0: // _S_empty_rep_storage, to represent empty strings.  When an operation such
michael@0: // as assignment or destruction is performed on a string, causing its existing
michael@0: // data member to be invalidated, it must not be freed if this static data
michael@0: // member is being used.  Otherwise, it counts as an attempt to free static
michael@0: // (and not allocated) data, which is a memory error.
michael@0: //
michael@0: // Generally, due to C++ template magic, _S_empty_rep_storage will be marked
michael@0: // as a coalesced symbol, meaning that the linker will combine multiple
michael@0: // instances into a single one when generating output.
michael@0: //
michael@0: // If a string class is used by multiple shared libraries, a problem occurs.
michael@0: // Each library will get its own copy of _S_empty_rep_storage.  When strings
michael@0: // are passed across a library boundary for alteration or destruction, memory
michael@0: // errors will result.  GNU libstdc++ contains a configuration option,
michael@0: // --enable-fully-dynamic-string (_GLIBCXX_FULLY_DYNAMIC_STRING), which
michael@0: // disables the static data member optimization, but it's a good optimization
michael@0: // and non-STL code is generally at the mercy of the system's STL
michael@0: // configuration.  Fully-dynamic strings are not the default for GNU libstdc++
michael@0: // libstdc++ itself or for the libstdc++ installations on the systems we care
michael@0: // about, such as Mac OS X and relevant flavors of Linux.
michael@0: //
michael@0: // See also http://gcc.gnu.org/bugzilla/show_bug.cgi?id=24196 .
michael@0: //
michael@0: // To avoid problems, string classes need to be explicitly instantiated only
michael@0: // once, in exactly one library.  All other string users see it via an "extern"
michael@0: // declaration.  This is precisely how GNU libstdc++ handles
michael@0: // std::basic_string<char> (string) and std::basic_string<wchar_t> (wstring).
michael@0: //
michael@0: // This also works around a Mac OS X linker bug in ld64-85.2.1 (Xcode 3.1.2),
michael@0: // in which the linker does not fully coalesce symbols when dead code
michael@0: // stripping is enabled.  This bug causes the memory errors described above
michael@0: // to occur even when a std::basic_string<> does not cross shared library
michael@0: // boundaries, such as in statically-linked executables.
michael@0: //
michael@0: // TODO(mark): File this bug with Apple and update this note with a bug number.
michael@0: 
michael@0: extern template class std::basic_string<char16, base::string16_char_traits>;
michael@0: 
michael@0: typedef std::basic_string<char16, base::string16_char_traits> string16;
michael@0: 
michael@0: extern std::ostream& operator<<(std::ostream& out, const string16& str);
michael@0: 
michael@0: #endif  // WCHAR_T_IS_UTF32
michael@0: 
michael@0: #endif  // BASE_STRING16_H_