char_traits.h

gcc-you can use this code to learn something about gcc, and inquire further into linux,

// Character Traits for use by standard string and iostream -*- C++ -*-

// Copyright (C) 1997, 1998, 1999, 2000, 2001, 2002
// Free Software Foundation, Inc.
//
// This file is part of the GNU ISO C++ Library.  This library is free
// software; you can redistribute it and/or modify it under the
// terms of the GNU General Public License as published by the
// Free Software Foundation; either version 2, or (at your option)
// any later version.

// This library is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.

// You should have received a copy of the GNU General Public License along
// with this library; see the file COPYING.  If not, write to the Free
// Software Foundation, 59 Temple Place - Suite 330, Boston, MA 02111-1307,
// USA.

// As a special exception, you may use this file as part of a free software
// library without restriction.  Specifically, if other files instantiate
// templates or use macros or inline functions from this file, or you compile
// this file and link it with other files to produce an executable, this
// file does not by itself cause the resulting executable to be covered by
// the GNU General Public License.  This exception does not however
// invalidate any other reasons why the executable file might be covered by
// the GNU General Public License.

//
// ISO C++ 14882: 21  Strings library
//

/** @file char_traits.h
 *  This is an internal header file, included by other library headers.
 *  You should not attempt to use it directly.
 */

#ifndef _CPP_BITS_CHAR_TRAITS_H
#define _CPP_BITS_CHAR_TRAITS_H 1

#pragma GCC system_header

#include <cstring>            // For memmove, memset, memchr
#include <bits/fpos.h>        // For streampos

namespace std 
{
  // 21.1
  /**
   *  @brief  Basis for explicit traits specializations.
   *
   *  @note  For any given actual character type, this definition is
   *  probably wrong.
   *
   *  See http://gcc.gnu.org/onlinedocs/libstdc++/21_strings/howto.html#5
   *  for advice on how to make use of this class for "unusual" character
   *  types.
  */
  template<class _CharT>
    struct char_traits
    {
      typedef _CharT 		char_type;
      // Unsigned as wint_t is unsigned.
      typedef unsigned long  	int_type;
      typedef streampos 	pos_type;
      typedef streamoff 	off_type;
      typedef mbstate_t 	state_type;
      
      static void 
      assign(char_type& __c1, const char_type& __c2);

      static bool 
      eq(const char_type& __c1, const char_type& __c2);

      static bool 
      lt(const char_type& __c1, const char_type& __c2);

      static int 
      compare(const char_type* __s1, const char_type* __s2, size_t __n);

      static size_t
      length(const char_type* __s);

      static const char_type* 
      find(const char_type* __s, size_t __n, const char_type& __a);

      static char_type* 
      move(char_type* __s1, const char_type* __s2, size_t __n);

      static char_type* 
      copy(char_type* __s1, const char_type* __s2, size_t __n);

      static char_type* 
      assign(char_type* __s, size_t __n, char_type __a);

      static char_type 
      to_char_type(const int_type& __c);

      static int_type 
      to_int_type(const char_type& __c);

      static bool 
      eq_int_type(const int_type& __c1, const int_type& __c2);

      static int_type 
      eof(); 

      static int_type 
      not_eof(const int_type& __c);
    };


  /// 21.1.3.1  char_traits specializations
  template<>
    struct char_traits<char>
    {
      typedef char 		char_type;
      typedef int 	        int_type;
      typedef streampos 	pos_type;
      typedef streamoff 	off_type;
      typedef mbstate_t 	state_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 memcmp(__s1, __s2, __n); }

      static size_t
      length(const char_type* __s)
      { return strlen(__s); }

      static const char_type* 
      find(const char_type* __s, size_t __n, const char_type& __a)
      { return static_cast<const char_type*>(memchr(__s, __a, __n)); }

      static char_type* 
      move(char_type* __s1, const char_type* __s2, size_t __n)
      { return static_cast<char_type*>(memmove(__s1, __s2, __n)); }

      static char_type* 
      copy(char_type* __s1, const char_type* __s2, size_t __n)
      {  return static_cast<char_type*>(memcpy(__s1, __s2, __n)); }

      static char_type* 
      assign(char_type* __s, size_t __n, char_type __a)
      { return static_cast<char_type*>(memset(__s, __a, __n)); }

      static char_type 
      to_char_type(const int_type& __c)
      { return static_cast<char_type>(__c); }

      // To keep both the byte 0xff and the eof symbol 0xffffffff
      // from ending up as 0xffffffff.
      static int_type 
      to_int_type(const char_type& __c)
      { return static_cast<int_type>(static_cast<unsigned char>(__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); }

      static int_type 
      not_eof(const int_type& __c)
      { return (__c == eof()) ? 0 : __c; }
  };


#ifdef _GLIBCPP_USE_WCHAR_T
  /// 21.1.3.2  char_traits specializations
  template<>
    struct char_traits<wchar_t>
    {
      typedef wchar_t 		char_type;
      typedef wint_t 		int_type;
      typedef streamoff 	off_type;
      typedef wstreampos 	pos_type;
      typedef mbstate_t 	state_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 wmemcmp(__s1, __s2, __n); }

      static size_t
      length(const char_type* __s)
      { return wcslen(__s); }

      static const char_type* 
      find(const char_type* __s, size_t __n, const char_type& __a)
      { return wmemchr(__s, __a, __n); }

      static char_type* 
      move(char_type* __s1, const char_type* __s2, int_type __n)
      { return wmemmove(__s1, __s2, __n); }

      static char_type* 
      copy(char_type* __s1, const char_type* __s2, size_t __n)
      { return wmemcpy(__s1, __s2, __n); }

      static char_type* 
      assign(char_type* __s, size_t __n, char_type __a)
      { return wmemset(__s, __a, __n); }

      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>(WEOF); }

      static int_type 
      not_eof(const int_type& __c)
      { return eq_int_type(__c, eof()) ? 0 : __c; }
  };
#endif //_GLIBCPP_USE_WCHAR_T

  template<typename _CharT, typename _Traits>
    struct _Char_traits_match
    {
      _CharT _M_c;
      _Char_traits_match(_CharT const& __c) : _M_c(__c) { }

      bool 
      operator()(_CharT const& __a) { return _Traits::eq(_M_c, __a); }
    };
} // namespace std

#endif