int GB.strcasecmp ( const char *s1 , const char *s2 )

This is a locale insensitive replacement for the glibc strcasecmp() function.

You must use this function instead of the standard glibc one to compare ASCII strings in a case unsensitive way, because the glibc one is localization aware. And if you did not know yet, in turkish, strcasecmp("i", "I") != 0.