<wctype.h>

<wctype.h> provides wide-character classification (iswalpha, iswdigit, iswspace) and case conversion (towupper, towlower). These functions work on full Unicode via wchar_t, unlike <ctype.h> which handles only ASCII.

Results depend on locale; call setlocale(LC_ALL, "") for correct Unicode support.

This example classifies and case-converts wide characters in a string.

// compile: gcc -o wctypeexample wctypeexample.c
// run: ./wctypeexample
// description: classify and case-convert wide characters
 
#include <wctype.h>
#include <wchar.h>
#include <locale.h>
 
int main() {
    setlocale(LC_ALL, "");
 
    const wchar_t* s = L"héLLo 42!";
    for (const wchar_t* p = s; *p; p++) {
        wprintf(L"'%lc'  alpha=%d  digit=%d  upper=%d  upper→%lc\n",
                *p,
                iswalpha(*p) != 0,
                iswdigit(*p) != 0,
                iswupper(*p) != 0,
                towupper(*p));
    }
 
    return 0;
}

Character classification (return non-zero if true):

• iswalpha(c): letter
• iswdigit(c): decimal digit
• iswalnum(c): alphanumeric
• iswspace(c): whitespace
• iswpunct(c): punctuation
• iswprint(c): printable
• iswcntrl(c): control character
• iswupper(c): uppercase
• iswlower(c): lowercase
• iswxdigit(c): hex digit

Case conversion:

• towupper(c): convert to uppercase
• towlower(c): convert to lowercase
• towctrans(c, trans): apply locale-specific transform

Locale-specific classification:

• wctype(name): get character class by name
• iswctype(c, type): test membership in class