strncasecmp.c

标准c库代码,可以应用于各个系统提供了大量的基本函数

/*
FUNCTION
	<<strncasecmp>>---case insensitive character string compare
	
INDEX
	strncasecmp

ANSI_SYNOPSIS
	#include <string.h>
	int strncasecmp(const char *<[a]>, const char * <[b]>, size_t <[length]>);

TRAD_SYNOPSIS
	#include <string.h>
	int strncasecmp(<[a]>, <[b]>, <[length]>)
	char *<[a]>;
	char *<[b]>;
	size_t <[length]>

DESCRIPTION
	<<strncasecmp>> compares up to <[length]> characters
	from the string at <[a]> to the string at <[b]> in a 
	case-insensitive manner.

RETURNS

	If <<*<[a]>>> sorts lexicographically after <<*<[b]>>> (after
	both are converted to upper case), <<strncasecmp>> returns a
	number greater than zero.  If the two strings are equivalent,
	<<strncasecmp>> returns zero.  If <<*<[a]>>> sorts
	lexicographically before <<*<[b]>>>, <<strncasecmp>> returns a
	number less than zero.

PORTABILITY
<<strncasecmp>> is in the Berkeley Software Distribution.

<<strncasecmp>> requires no supporting OS subroutines. It uses
toupper() from elsewhere in this library.

QUICKREF
	strncasecmp
*/

#include <string.h>
#include <ctype.h>

int 
_DEFUN (strncasecmp, (s1, s2, n),
	_CONST char *s1 _AND
	_CONST char *s2 _AND
	size_t n)
{
  if (n == 0)
    return 0;

  while (n-- != 0 && toupper(*s1) == toupper(*s2))
    {
      if (n == 0 || *s1 == '\0' || *s2 == '\0')
	break;
      s1++;
      s2++;
    }

  return toupper(*(unsigned char *) s1) - toupper(*(unsigned char *) s2);
}