toupper man page

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).

InterfaceAttributeValue
toupper(), tolower(),
toupper_l(), tolower_l()
Thread safetyMT-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.

See Also

isalpha(3), newlocale(3), setlocale(3), towlower(3), towupper(3), uselocale(3), locale(7)

Colophon

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Referenced By

duplocale(3), isalpha(3), locale(7), toascii(3), towlower(3), towupper(3), unicode::tolower(3), wctrans(3).

tolower(3), tolower_l(3) and toupper_l(3) are aliases of toupper(3).

2016-10-08 GNU Linux Programmer's Manual