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tolower(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.
   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 4.09 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/.



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