tolower (3)
Leading comments
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NAME
toupper, tolower, toupper_l, tolower_l - convert uppercase or lowercaseSYNOPSIS
#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 a 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 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.