TOUPPER
Section: Linux Programmer's Manual (3)
Updated: 2017-09-15
Index
Return to Main Contents
NAME
toupper, tolower, toupper_l, tolower_l - convert uppercase or lowercase
SYNOPSIS
#include <ctype.h>
int toupper(int c);
int tolower(int c);
int toupper_l(int c, locale_t locale);
int tolower_l(int c, locale_t locale);
Feature Test Macro Requirements for glibc (see
feature_test_macros(7)):
toupper_l(),
tolower_l():
-
- Since glibc 2.10:
-
_XOPEN_SOURCE >= 700
- Before glibc 2.10:
-
_GNU_SOURCE
DESCRIPTION
These functions convert lowercase letters to uppercase, and vice versa.
If
c
is a lowercase letter,
toupper()
returns its uppercase equivalent,
if an uppercase representation exists in the current locale.
Otherwise, it returns
c.
The
toupper_l()
function performs the same task,
but uses the locale referred to by the locale handle
locale.
If
c
is an uppercase letter,
tolower()
returns its lowercase equivalent,
if a lowercase representation exists in the current locale.
Otherwise, it returns
c.
The
tolower_l()
function performs the same task,
but uses the locale referred to by the locale handle
locale.
If
c
is neither an
unsigned char
value nor
EOF,
the behavior of these functions
is undefined.
The behavior of
toupper_l()
and
tolower_l()
is undefined if
locale
is the special locale object
LC_GLOBAL_LOCALE
(see
duplocale(3))
or is not a valid locale object handle.
RETURN VALUE
The value returned is that of the converted letter, or
c
if the conversion was not possible.
ATTRIBUTES
For an explanation of the terms used in this section, see
attributes(7).
| Interface | Attribute | Value
|
toupper(),
tolower(),
toupper_l(),
tolower_l()
| Thread safety | MT-Safe
|
CONFORMING TO
toupper(),
tolower():
C89, C99, 4.3BSD, POSIX.1-2001, POSIX.1-2008.
toupper_l(),
tolower_l():
POSIX.1-2008.
NOTES
The standards require that the argument
c
for these functions is either
EOF
or a value that is representable in the type
unsigned char.
If the argument
c
is of type
char,
it must be cast to
unsigned char,
as in the following example:
char c;
...
res = toupper((unsigned char) c);
This is necessary because
char
may be the equivalent
signed char,
in which case a byte where the top bit is set would be sign extended when
converting to
int,
yielding a value that is outside the range of
unsigned char.
The details of what constitutes an uppercase or lowercase letter depend
on the 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.
SEE ALSO
isalpha(3),
newlocale(3),
setlocale(3),
towlower(3),
towupper(3),
uselocale(3),
locale(7)
COLOPHON
This page is part of release 4.13 of the Linux
man-pages
project.
A description of the project,
information about reporting bugs,
and the latest version of this page,
can be found at
https://www.kernel.org/doc/man-pages/.
Index
- NAME
-
- SYNOPSIS
-
- DESCRIPTION
-
- RETURN VALUE
-
- ATTRIBUTES
-
- CONFORMING TO
-
- NOTES
-
- SEE ALSO
-
- COLOPHON
-
|
|
- Running on 
-
:
: 