php man page for 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.  Oth-
       erwise, 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.   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 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/.

GNU
								    2017-09-15								TOUPPER(3)