toupper (3)

#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

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.

The value returned is that of the converted letter, or c if the conversion was not possible.

Multithreading (see pthreads(7))

The toupper() and tolower() functions are thread-safe with exceptions. These functions can be safely used in multithreaded applications, as long as setlocale(3) is not called to change the locale during their execution.

toupper(), tolower(): C89, C99, 4.3BSD, POSIX.1-2001, POSIX.1-2008.

toupper_l(), tolower_l(): POSIX.1-2008.

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.

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

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