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man:toupper

TOUPPER(3) Linux Programmer's Manual TOUPPER(3)

NAME

     toupper, tolower, toupper_l, tolower_l - convert uppercase or lowercase

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
     attributes(7).
     +-------------------------+---------------+---------+
     |Interface                | Attribute     | Value   |
     +-------------------------+---------------+---------+
     |toupper(), tolower(),    | Thread safety | MT-Safe |
     |toupper_l(), tolower_l() |               |         |
     +-------------------------+---------------+---------+

CONFORMING TO

     toupper(), tolower(): C89, 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
     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 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)

COLOPHON

     This  page  is  part of release 4.16 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 2017-09-15 TOUPPER(3)

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