strcasecmp.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.
//
//  strcasecmp.c
//

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

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


int strcasecmp(const char *s1, const char *s2)
{
  // The strcasecmp() function compares the two strings s1 and s2,
  // ignoring the case of the characters.  It returns an integer less than,
  // equal to, or greater than zero if s1 is found, respectively, to be less
  // than, to match, or be greater than s2.

  int count = 0;

  for (count = 0; count < MAXSTRINGLENGTH; count ++)
    {
      if ((s1[count] == '\0') && (s2[count] == '\0'))
	// The strings match
	return (0);

      // Is the ascii code a lowercase alphabet character?
      else if ((s1[count] >= (char) 97) &&
	       (s1[count] <= (char) 122) &&
	       (s2[count] == (s1[count] - (char) 32)))
	// We call it a match
	continue;

      // Is the ascii code an uppercase alphabet character?
      else if ((s1[count] >= (char) 65) &&
	       (s1[count] <= (char) 90) &&
	       (s2[count] == (s1[count] + (char) 32)))
	// We call it a match
	continue;

      else if (s1[count] != s2[count])
	{
	  // The strings stop matching here.

	  // Is one of the characters a NULL character?  If so, that string
	  // is 'less than' the other
	  if (s1[count] == '\0')
	    return (-1);
	  else if (s2[count] == '\0')
	    return (1);

	  // Otherwise, is the s1 character in question 'less than' or
	  // 'greater than' the s2 character?  This will return a positive
	  // number if the s1 character is greater than s2, else a negative
	  // number.
	  return (s1[count] - s2[count]);
	}
    }

  // EEK, we have an overflow, but the strings match up to this point.
  // I'm not sure what the 'correct' thing to do is, but return 'equal'
  // anyway, whilst setting errno
  errno = ERR_BOUNDS;
  return (0);
}