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.  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.

RETURN VALUE

       The  value  returned  is  that  of  the  converted  letter, or c if the conversion 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  corresponding  uppercase
       equivalent; the German sharp s is one example.

SEE ALSO

       isalpha(3), newlocale(3), setlocale(3), towlower(3), towupper(3), uselocale(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/.