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)):
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 (), toupper_l (), tolower_l () |
Thread safety |
MT-Safe |
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)