strncpy.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.
//
//  strncpy.c
//

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

// Here is the description from the GNU man pages:
// The strncpy() function is similar [to strcpy], except that not more
// than n bytes of src are copied. Thus, if there is no null byte among the
// first n bytes of src, the result wil not be null-terminated.

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


char *strncpy(char *destString, const char *sourceString, size_t maxLength)
{
  unsigned count;

  // Make sure neither of the pointers are NULL
  if ((destString == (char *) NULL) || (sourceString == (char *) NULL))
    {
      errno = ERR_NULLPARAMETER;
      return (destString = NULL);
    }

  if (maxLength > MAXSTRINGLENGTH)
    maxLength = MAXSTRINGLENGTH;

  for (count = 0; count < maxLength; count ++)
    {
      destString[count] = sourceString[count];
      
      if (sourceString[count] == '\0')
	break;
    }

  // 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 (count >= MAXSTRINGLENGTH)
    {
      errno = ERR_BOUNDS;
      return (destString = NULL);
    }

  // Return success
  return (destString);
}