toupper, tolower, toupper_l, tolower_l - convert uppercase or lowercase
#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)):
Since glibc 2.10: _XOPEN_SOURCE >= 700 Before glibc 2.10: _GNU_SOURCE
These functions convert lowercase letters to uppercase, and vice versa.
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
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
c is neither an
unsigned char value nor EOF, the behavior of these functions is undefined.
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).
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
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.
This page is part of release 4.15 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/.