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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ATTRIBUTES | CONFORMING TO | NOTES | SEE ALSO | COLOPHON |
TOUPPER(3) Linux Programmer's Manual TOUPPER(3)
toupper, tolower, toupper_l, tolower_l - convert uppercase or lower‐
case
#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 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.
The value returned is that of the converted letter, or c if the
conversion was not possible.
For an explanation of the terms used in this section, see
attributes(7).
┌─────────────────────────┬───────────────┬─────────┐
│Interface │ Attribute │ Value │
├─────────────────────────┼───────────────┼─────────┤
│toupper(), tolower(), │ Thread safety │ MT-Safe │
│toupper_l(), tolower_l() │ │ │
└─────────────────────────┴───────────────┴─────────┘
toupper(), tolower(): C89, C99, 4.3BSD, POSIX.1-2001, POSIX.1-2008.
toupper_l(), tolower_l(): POSIX.1-2008.
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
unsigned 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
corresponding uppercase equivalent; the German sharp s is one
example.
isalpha(3), newlocale(3), setlocale(3), towlower(3), towupper(3),
uselocale(3), locale(7)
This page is part of release 4.12 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the
latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
GNU 2016-10-08 TOUPPER(3)
Pages that refer to this page: duplocale(3), isalpha(3), toascii(3), towlower(3), towupper(3), wctrans(3), locale(7)