'\" t
.\" Copyright (c) 1993 by Thomas Koenig (ig25@rz.uni-karlsruhe.de)
.\" and Copyright 2014 Michael Kerrisk <mtk.manpages@gmail.com>
.\"
.\" SPDX-License-Identifier: Linux-man-pages-copyleft
.\"
.\" 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 2023-07-20 "Linux man-pages 6.05.01"
.SH NAME
toupper, tolower, toupper_l, tolower_l \- convert uppercase or lowercase
.SH LIBRARY
Standard C library
.RI ( libc ", " \-lc )
.SH SYNOPSIS
.nf
.B #include <ctype.h>
.PP
.BI "int toupper(int " "c" );
.BI "int tolower(int " "c" );
.PP
.BI "int toupper_l(int " c ", locale_t " locale );
.BI "int tolower_l(int " c ", locale_t " locale );
.fi
.PP
.RS -4
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.RE
.PP
.BR toupper_l (),
.BR tolower_l ():
.nf
    Since glibc 2.10:
        _XOPEN_SOURCE >= 700
    Before glibc 2.10:
        _GNU_SOURCE
.fi
.SH DESCRIPTION
These functions convert lowercase letters to uppercase, and vice versa.
.PP
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 .
.PP
If
.I c
is an 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.
.PP
The behavior of
.BR toupper_l ()
and
.BR tolower_l ()
is undefined if
.I locale
is the special locale object
.B 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
For an explanation of the terms used in this section, see
.BR attributes (7).
.TS
allbox;
lbx lb lb
l l l.
Interface	Attribute	Value
T{
.na
.nh
.BR toupper (),
.BR tolower (),
.BR toupper_l (),
.BR tolower_l ()
T}	Thread safety	MT-Safe
.TE
.sp 1
.SH STANDARDS
.TP
.BR toupper ()
.TQ
.BR tolower ()
C11, POSIX.1-2008.
.TP
.BR toupper_l ()
.TQ
.BR tolower_l ()
POSIX.1-2008.
.SH HISTORY
.TP
.BR toupper ()
.TQ
.BR tolower ()
C89, 4.3BSD, POSIX.1-2001.
.TP
.BR toupper_l ()
.TQ
.BR tolower_l ()
POSIX.1-2008.
.SH NOTES
The standards require that the argument
.I c
for these functions is either
.B EOF
or a value that is representable in the type
.IR "unsigned char" .
If the argument
.I c
is of type
.IR char ,
it must be cast to
.IR "unsigned char" ,
as in the following example:
.PP
.in +4n
.EX
char c;
\&...
res = toupper((unsigned char) c);
.EE
.in
.PP
This is necessary because
.I char
may be the equivalent
.IR "signed char" ,
in which case a byte where the top bit is set would be sign extended when
converting to
.IR int ,
yielding a value that is outside the range of
.IR "unsigned char" .
.PP
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 towlower (3),
.BR towupper (3),
.BR uselocale (3),
.BR locale (7)