LCOV - code coverage report
Current view: directory - ipc/chromium/src/base - string16.h (source / functions) Found Hit Coverage
Test: app.info Lines: 17 0 0.0 %
Date: 2012-06-02 Functions: 8 0 0.0 %

       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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