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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 4.15 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/.
GNU                               2017-09-15                        TOUPPER(3)