Originální popis anglicky:
toupper, tolower - convert letter to upper or lower case
Návod, kniha: Linux Programmer's Manual
#include <ctype.h>
int toupper(int c);
int tolower(int c);
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.
The value returned is that of the converted letter, or
c if the
conversion was not possible.
ANSI C, BSD 4.3
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),
locale(7)
