toupper, tolower, toupper_l, tolower_l - convert uppercase or lowercase
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)):
Since glibc 2.10:
_XOPEN_SOURCE >= 700
Before glibc 2.10:
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
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),
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