toupper

toupper, tolower - convert letter to upper or lower case

#include <ctype.h>
 I int toupper(int  c );

I int tolower(int  c );

R toupper () converts the letter c to upper case, if possible.

R tolower () converts the letter c to lower case, if possible.

If c is not an unsigned char value, or EOF, the behavior of these functions is undefined.

The value returned is that of the converted letter, or c if the conversion was not possible.

C89, C99, 4.3BSD

The details of what constitutes an uppercase or lowercase letter depend on the current locale. For example, the default C locale does not know about umlauts, so no conversion is done for them.

In some non-English locales, there are lowercase letters with no corresponding uppercase equivalent; the German sharp s is one example.

isalpha(3), setlocale(3), towlower(3), towupper(3), locale(7)