strcasestr.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.
//
//  strcasestr.c
//

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

#include <string.h>


char *strcasestr(const char *s1, const char *s2)
{
  // The strcasestr() function finds the first occurrence of the substring s2
  // in the string s1, ignoring case.  The terminating `\0' characters are not
  // compared.  The strcasestr() function returns a pointer to the beginning of
  // the substring, or NULL if the substring is not found.

  int count = 0;
  char *ptr = NULL;
  int s1_length = strlen(s1);
  int s2_length = strlen(s2);

  ptr = (char *) s1;

  for (count = 0; count < s1_length; count ++)
    {
      if (!strncasecmp(ptr, s2, s2_length))
	return (ptr);
      else
	ptr++;
    }

  // Not found
  return (ptr = NULL);
}