int strcasecmp(const char *s1, const char *s2);
strcasecmp compares the string pointed to by s1 to the string pointed to by s2 ignoring differences in case. strcasecmp returns an integer greater than, equal to, or less than zero if the string pointed to by s1 is greater than, equal to, or less than the string pointed to by s2.
strcasecmp conforms to POSIX.1-2008.