//en.cppreference.com/w/c/string/wide/towupper.html
#include <stdio.h>
#include <wchar.h>
#include <wctype.h>
#include <locale.h>
int main(void)
{
wchar_t wc = L'\u017f'; // Latin small letter Long S ('ſ')
printf("in the default locale, towupper(%#x) = %#x\n", wc, towupper(wc));
setlocale(LC_ALL, "en_US.utf8");
printf("in Unicode locale, towupper(%#x) = %#x\n", wc, towupper(wc));
}