toupper(3) Library Functions Manual toupper(3)
NAME
toupper, tolower, toupper_l, tolower_l - convert uppercase or lowercase
LIBRARY
Standard C library (libc, -lc)
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. Other-
wise, 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 equiva-
lent, if a lowercase representation exists in the current locale. Oth-
erwise, 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 conver-
sion was not possible.
ATTRIBUTES
For an explanation of the terms used in this section, see at-
tributes(7).
┌────────────────────────────────────────────┬───────────────┬─────────┐
│Interface │ Attribute │ Value │
├────────────────────────────────────────────┼───────────────┼─────────┤
│toupper(), tolower(), toupper_l(), │ Thread safety │ MT-Safe │
│tolower_l() │ │ │
└────────────────────────────────────────────┴───────────────┴─────────┘
STANDARDS
toupper(), tolower(): 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 un-
signed 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 corre-
sponding uppercase equivalent; the German sharp s is one example.
SEE ALSO
isalpha(3), newlocale(3), setlocale(3), towlower(3), towupper(3), use-
locale(3), locale(7)
Linux man-pages 6.03 2022-12-29 toupper(3)
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