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WCSCASECMP(3) Library Functions Manual WCSCASECMP(3)

wcscasecmp, wcscasecmp_l, wcsncasecmp, wcsncasecmp_l
compare wide strings, ignoring case

#include <wchar.h>
wcscasecmp(const wchar_t *s1, const wchar_t *s2);
wcscasecmp_l(const wchar_t *s1, const wchar_t *s2, locale_t locale);
wcsncasecmp(const wchar_t *s1, const wchar_t *s2, size_t len);
wcsncasecmp_l(const wchar_t *s1, const wchar_t *s2, size_t len, locale_t locale);

These functions compare the wide strings s1 and s2 and return an integer greater than, equal to, or less than 0, according to whether s1 is lexicographically greater than, equal to, or less than s2 after translation of each corresponding wide character to lower case. The wide strings themselves are not modified.
For the translation to lower case, wcscasecmp() and wcsncasecmp() use the thread-specific locale as defined with uselocale(3), falling back to the global locale defined with setlocale(3). wcscasecmp_l() and wcsncasecmp_l() use the locale argument instead.
wcsncasecmp() and wcsncasecmp_l() compare at most len wide characters.

newlocale(3), setlocale(3), strcasecmp(3), wcscmp(3), wmemcmp(3)

These functions conform to IEEE Std 1003.1-2008 (“POSIX.1”).

The wcscasecmp() and wcsncasecmp() functions have been available since OpenBSD 5.0, and wcscasecmp_l() and wcsncasecmp_l() since OpenBSD 6.2.

The OpenBSD versions of wcscasecmp() and wcsncasecmp() were implemented by Marc Espie <espie@openbsd.org>.
September 5, 2017 OpenBSD-current