strncat.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.
//
//  strncat.c
//

// This is the standard "strncat" function, as found in standard C libraries
// The strncat() function appends the first n characters of the source string
// to the dest string overwriting the `\0' character at the end of dest, and
// then adds a terminating `\0' character.  The strings may not overlap, and
// the dest string must have enough space for the result.


#include <string.h>
#include <errno.h>


char *strncat(char *destString, const char *sourceString, size_t maxLength)
{
  unsigned count1, count2;
  int endFlag = 0;
  char sourceChar;
  
  // Find the end of the first String
  for (count1 = 0; count1 < MAXSTRINGLENGTH; )
    {
      if (destString[count1] == '\0')
	break;
      else
	count1++;
    }

  // If this is true, then we probably have an unterminated string
  // constant.  Checking for a string that exceeds MAXSTRINGLENGTH will
  // help to prevent the routine from running off too far into memory.
  if (count1 >= MAXSTRINGLENGTH)
    {
      errno = ERR_BOUNDS;
      return (destString = NULL);
    }

  // Now copy the source string into the dest.  If source is shorter than
  // maxLength, pad dest with NULL characters.
  for (count2 = 0; count2 < maxLength; )
    {
      if ((sourceString[count2] == '\0') || (endFlag == 1))
	{
	  endFlag = 1;
	  sourceChar = (char) NULL;
	}
      
      else
	sourceChar = sourceString[count2];

      destString[count1] = sourceChar;
      count1++; count2++;
    }

  // Make sure there's a NULL at the end
  destString[count1] = NULL;

  // Return success
  return (destString);
}