string 函数
strcasecmp
忽略大小写的比较函数
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| #include <strings.h>
int strcasecmp (const char *s1, const char *s2);
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strcasecmp()用来比较参数s1 和s2 字符串，比较时会自动忽略大小写的差异。
返回值：若参数s1 和s2 字符串相同则返回0。s1 长度大于s2 长度则返回大于0 的值，s1 长度若小于s2 长度则返回小于0 的值。
glibc-2.32中函数实现
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| /* Compare S1 and S2, ignoring case, returning less than, equal to or
greater than zero if S1 is lexicographically less than,
equal to or greater than S2. */
int
__strcasecmp (const char *s1, const char *s2 LOCALE_PARAM)
{
#if defined _LIBC && !defined USE_IN_EXTENDED_LOCALE_MODEL
locale_t loc = _NL_CURRENT_LOCALE;
#endif
const unsigned char *p1 = (const unsigned char *) s1;
const unsigned char *p2 = (const unsigned char *) s2;
int result;
if (p1 == p2)
return 0;
while ((result = TOLOWER (*p1) - TOLOWER (*p2++)) == 0)
if (*p1++ == '\0')
break;
return result;
}
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