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2017-09-15
Aliases: tolower(3), tolower(3), tolower(3), tolower(3), tolower(3), tolower(3), tolower(3), tolower(3), tolower(3), tolower(3), tolower(3), tolower(3), tolower_l(3), tolower_l(3), tolower_l(3), tolower_l(3), tolower_l(3), tolower_l(3), tolower_l(3), tolower_l(3), tolower_l(3), tolower_l(3), toupper_l(3), toupper_l(3), toupper_l(3), toupper_l(3), toupper_l(3), toupper_l(3), toupper_l(3), toupper_l(3), toupper_l(3), toupper_l(3)

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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

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.

COLOPHON

This page is part of release 5.00 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/.
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