mbstowcs.c

上一个上传的有问题,这个是好的。visopsys包括系统内核和GUI的全部SOURCE code ,还包括一些基本的docs文档。里面src子目录对应所有SOURCE code.对于想研究操作系统的朋

// 
//  Visopsys
//  Copyright (C) 1998-2007 J. Andrew McLaughlin
//  
//  This library is free software; you can redistribute it and/or modify it
//  under the terms of the GNU Lesser General Public License as published by
//  the Free Software Foundation; either version 2.1 of the License, 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 Lesser
//  General Public License for more details.
//
//  You should have received a copy of the GNU Lesser General Public License
//  along with this library; if not, write to the Free Software Foundation,
//  Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
//
//  mbstowcs.c
//

// This is the standard "mbstowcs" function, as found in standard C libraries

#include <stdlib.h>


size_t mbstowcs(wchar_t *dest, const char *src, size_t n)
{
  // Here's how the Linux man page describes this function (oh boy):
  // 
  // If dest is not a NULL pointer, the mbstowcs function converts the
  // multibyte string src to a wide-character string starting at dest.  At
  // most n wide characters are written to dest.  The conversion starts in
  // the initial state.  The conversion can stop for three reasons:
  //
  // 1. An invalid multibyte sequence has been encountered.  In this case
  // (size_t)(-1) is returned.
  //
  // 2. n non-L'\0' wide characters have been stored at dest.  In this case
  // the number of wide characters written to dest is returned, but the
  // shift state at this point is lost.
  //
  // 3.  The  multibyte  string has been completely converted, including the
  // terminating '\0'.  In this case the number of wide characters written to
  // dest, excluding the terminating L'\0' character, is returned.
  //
  // The programmer must ensure that there is room for at least n wide
  // characters at dest.
  // 
  // If dest is NULL, n is ignored, and the conversion  proceeds as above,
  // except that the converted wide characters are not written out to memory,
  // and that no length limit exists.
  // 
  // In order to avoid the case 2 above, the programmer should make sure n
  // is greater or equal to mbstowcs(NULL,src,0)+1.
  //
  // We're going to attempt to support UTF-8 as our multibyte standard.

  int numBytes = 0;
  int maxBytes = (n * MB_CUR_MAX);
  size_t count;

  for (count = 0; count < n; count ++)
    {
      numBytes = mbtowc(dest, src, maxBytes);

      if (numBytes < 0)
	return (-1);

      if (*dest == (wchar_t) NULL)
	return (count);

      dest += 1;
      src += numBytes;
      maxBytes -= numBytes;
    }

  return (n);
}