.\" Copyright (c) 1993 by Thomas Koenig (ig25@rz.uni-karlsruhe.de)
.\" and Copyright 2014 Michael Kerrisk <mtk.manpages@gmail.com>
.\"
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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  2014-03-18 "GNU" "Linux Programmer's Manual"
.SH NAME
toupper, tolower, toupper_l, tolower_l \- convert uppercase or lowercase
.SH SYNOPSIS
.nf
.B #include <ctype.h>
.sp
.BI "int toupper(int " "c" );
.br
.BI "int tolower(int " "c" );

.BI "int toupper_l(int " c ", locale_t " locale );
.BI "int tolower_l(int " c ", locale_t " locale );
.fi
.sp
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.in
.sp
.BR toupper_l (),
.BR tolower_l ():
.PD 0
.RS 4
.TP
Since glibc 2.10:
_XOPEN_SOURCE\ >=\ 700
.TP
Before glibc 2.10:
_GNU_SOURCE
.RE
.PD
.SH DESCRIPTION
These functions convert lowercase letters to uppercase, and vice versa.

If
.I c
is a lowercase letter,
.BR toupper ()
returns its uppercase equivalent,
if an uppercase representation exists in the current locale.
Otherwise, it returns
.IR c .
The
.BR toupper_l ()
function performs the same task,
but uses the locale referred to by the locale handle
.IR locale .

If
.I c
is a uppercase letter,
.BR tolower ()
returns its lowercase equivalent,
if a lowercase representation exists in the current locale.
Otherwise, it returns
.IR c .
The
.BR tolower_l ()
function performs the same task,
but uses the locale referred to by the locale handle
.IR locale .
.PP
If
.I c
is neither an
.I "unsigned char"
value nor
.BR EOF ,
the behavior of these functions
is undefined.

The behavior of
.BR toupper_l ()
and
.BR tolower_l ()
is undefined if
.I locale
is the special locale object
.BR LC_GLOBAL_LOCALE
(see
.BR duplocale (3))
or is not a valid locale object handle.
.SH RETURN VALUE
The value returned is that of the converted letter, or
.I c
if the conversion was not possible.
.SH ATTRIBUTES
.SS Multithreading (see pthreads(7))
The
.BR toupper ()
and
.BR tolower ()
functions are thread-safe with exceptions.
These functions can be safely used in multithreaded applications,
as long as
.BR setlocale (3)
is not called to change the locale during their execution.
.\" FIXME . Add toupper_l() and tolower_l()
.SH CONFORMING TO
.BR toupper (),
.BR tolower ():
C89, C99, 4.3BSD, POSIX.1-2001, POSIX.1-2008.

.BR toupper_l (),
.BR tolower_l ():
POSIX.1-2008.
.SH NOTES
The details of what constitutes an uppercase or lowercase letter depend
on the 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;
.\" FIXME One day the statement about "sharp s" needs to be reworked,
.\" since there is nowadays a capital "sharp s" that has a codepoint
.\" in Unicode 5.0; see https://en.wikipedia.org/wiki/Capital_%E1%BA%9E
the German sharp s is one example.
.SH SEE ALSO
.BR isalpha (3),
.BR newlocale (3),
.BR setlocale (3),
.BR uselocale (3),
.BR towlower (3),
.BR towupper (3),
.BR locale (7)
.SH COLOPHON
This page is part of release 3.74 of the Linux
.I man-pages
project.
A description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at
\%http://www.kernel.org/doc/man\-pages/.