linux和windows下不区分大小写的字符串比较

在写一个判断POST和GET时用到不区分大小写的字符串比较。

头文件都是string. h

windows平台：

函数：stricmp（char *str1, char *str2）, strnicmp(char *str1, char *str2, size_t n).

Linux平台：

函数：strcasecmp(char *str1, char *str2), strncasecmp(char *str1, char *str2, size_t n).

下面给出linux下两个函数的实现

#include <sys/cdefs.h>
#include <string.h>

#if defined(LIBC_SCCS) && !defined(lint)
static char sccsid[] = "@(#)strcasecmp.c	8.1 (Berkeley) 6/4/93";
#endif /* LIBC_SCCS and not lint */

typedef unsigned char u_char;

/*
 * This array is designed for mapping upper and lower case letter
 * together for a case independent comparison.  The mappings are
 * based upon ascii character sequences.
 */
static const u_char charmap[] = {
	'\000', '\001', '\002', '\003', '\004', '\005', '\006', '\007',
	'\010', '\011', '\012', '\013', '\014', '\015', '\016', '\017',
	'\020', '\021', '\022', '\023', '\024', '\025', '\026', '\027',
	'\030', '\031', '\032', '\033', '\034', '\035', '\036', '\037',
	'\040', '\041', '\042', '\043', '\044', '\045', '\046', '\047',
	'\050', '\051', '\052', '\053', '\054', '\055', '\056', '\057',
	'\060', '\061', '\062', '\063', '\064', '\065', '\066', '\067',
	'\070', '\071', '\072', '\073', '\074', '\075', '\076', '\077',
	'\100', '\141', '\142', '\143', '\144', '\145', '\146', '\147',
	'\150', '\151', '\152', '\153', '\154', '\155', '\156', '\157',
	'\160', '\161', '\162', '\163', '\164', '\165', '\166', '\167',
	'\170', '\171', '\172', '\133', '\134', '\135', '\136', '\137',
	'\140', '\141', '\142', '\143', '\144', '\145', '\146', '\147',
	'\150', '\151', '\152', '\153', '\154', '\155', '\156', '\157',
	'\160', '\161', '\162', '\163', '\164', '\165', '\166', '\167',
	'\170', '\171', '\172', '\173', '\174', '\175', '\176', '\177',
	'\200', '\201', '\202', '\203', '\204', '\205', '\206', '\207',
	'\210', '\211', '\212', '\213', '\214', '\215', '\216', '\217',
	'\220', '\221', '\222', '\223', '\224', '\225', '\226', '\227',
	'\230', '\231', '\232', '\233', '\234', '\235', '\236', '\237',
	'\240', '\241', '\242', '\243', '\244', '\245', '\246', '\247',
	'\250', '\251', '\252', '\253', '\254', '\255', '\256', '\257',
	'\260', '\261', '\262', '\263', '\264', '\265', '\266', '\267',
	'\270', '\271', '\272', '\273', '\274', '\275', '\276', '\277',
	'\300', '\301', '\302', '\303', '\304', '\305', '\306', '\307',
	'\310', '\311', '\312', '\313', '\314', '\315', '\316', '\317',
	'\320', '\321', '\322', '\323', '\324', '\325', '\326', '\327',
	'\330', '\331', '\332', '\333', '\334', '\335', '\336', '\337',
	'\340', '\341', '\342', '\343', '\344', '\345', '\346', '\347',
	'\350', '\351', '\352', '\353', '\354', '\355', '\356', '\357',
	'\360', '\361', '\362', '\363', '\364', '\365', '\366', '\367',
	'\370', '\371', '\372', '\373', '\374', '\375', '\376', '\377',
};

int
strcasecmp(s1, s2)
	const char *s1, *s2;
{
	register const u_char *cm = charmap,
			*us1 = (const u_char *)s1,
			*us2 = (const u_char *)s2;

	while (cm[*us1] == cm[*us2++])
		if (*us1++ == '\0')
			return (0);
	return (cm[*us1] - cm[*--us2]);
}

int
strncasecmp(s1, s2, n)
	const char *s1, *s2;
	register size_t n;
{
	if (n != 0) {
		register const u_char *cm = charmap,
				*us1 = (const u_char *)s1,
				*us2 = (const u_char *)s2;

		do {
			if (cm[*us1] != cm[*us2++])
				return (cm[*us1] - cm[*--us2]);
			if (*us1++ == '\0')
				break;
		} while (--n != 0);
	}
	return (0);
}