redhat man page for tolower

TOUPPER(3)						     Linux Programmer's Manual							TOUPPER(3)

NAME
       toupper, tolower - convert letter to upper or lower case

SYNOPSIS
       #include <ctype.h>

       int toupper(int c);
       int tolower(int c);

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

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

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

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

CONFORMING TO
       ANSI C, BSD 4.3

BUGS
       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.

SEE ALSO
       isalpha(3), setlocale(3), locale(7)

GNU
								    1993-04-04								TOUPPER(3)