//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));
}