.\" Copyright (c) 1993 by Thomas Koenig (ig25@rz.uni-karlsruhe.de)
.\"
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.\" Modified Sat Jul 24 17:45:39 1993 by Rik Faith (faith@cs.unc.edu)
.\" Modified 2000-02-13 by Nicolás Lichtmaier <nick@debian.org>
.TH TOUPPER 3  1993-04-04 "GNU" "Linux Programmer's Manual"
.SH NAME
toupper, tolower \- convert letter to upper or lower case
.SH SYNOPSIS
.nf
.B #include <ctype.h>
.sp
.BI "int toupper(int " "c" );
.br
.BI "int tolower(int " "c" );
.fi
.SH DESCRIPTION
.BR toupper ()
converts the letter
.I c
to upper case, if possible.
.PP
.BR tolower ()
converts the letter
.I c
to lower case, if possible.
.PP
If
.I c
is not an
.I "unsigned char"
value, or
.BR EOF ,
the behavior of these functions
is undefined.
.SH RETURN VALUE
The value returned is that of the converted letter, or
.I c
if the conversion was not possible.
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.TS
allbox;
lbw24 lb lb
l l l.
Interface	Attribute	Value
T{
.BR toupper (),
.BR tolower (),
.br
.BR toupper_l (),
.BR tolower_l ()
T}	Thread safety	MT-Safe
.TE
.SH CONFORMING TO
C89, C99, 4.3BSD.
.SH BUGS
The details of what constitutes an uppercase or lowercase letter depend
on the current locale.
For example, the default
.B """C"""
locale does not know about umlauts, so no conversion is done for them.
.PP
In some non-English locales, there are lowercase letters with no
corresponding uppercase equivalent; the German sharp s is one
example.
.SH SEE ALSO
.BR isalpha (3),
.BR setlocale (3),
.BR towlower (3),
.BR towupper (3),
.BR locale (7)
.SH COLOPHON
This page is part of release 3.53 of the Linux
.I man-pages
project.
A description of the project,
and information about reporting bugs,
can be found at
\%http://www.kernel.org/doc/man\-pages/.