Provided by: manpages-dev_3.21-1_all
toupper, tolower - convert letter to upper or lower case
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 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)
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be found at http://www.kernel.org/doc/man-pages/.