function_exists(3) [php man page]

FUNCTION_EXISTS(3)							 1							FUNCTION_EXISTS(3)

function_exists - Return TRUEif the given function has been defined

SYNOPSIS

       bool function_exists (string  $function_name)

DESCRIPTION

	Checks the list of defined functions, both built-in (internal) and user-defined, for $function_name.

PARAMETERS

	      o $function_name
		- The function name, as a string.

RETURN VALUES

	Returns TRUE if $function_name exists and is a function, FALSE otherwise.

       Note

	       This function will return FALSE for constructs, such as include_once(3) and echo(3).

EXAMPLES

       Example #1

	      function_exists(3) example

	      <?php
	      if (function_exists('imap_open')) {
		  echo "IMAP functions are available.<br />
";
	      } else {
		  echo "IMAP functions are not available.<br />
";
	      }
	      ?>

NOTES

       Note

	       A  function  name may exist even if the function itself is unusable due to configuration or compiling options (with the image func-
	      tions being an example).

SEE ALSO

       method_exists(3), is_callable(3), get_defined_functions(3), class_exists(3), extension_loaded(3).

PHP Documentation Group 													FUNCTION_EXISTS(3)

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DEFINED(3)								 1								DEFINED(3)

defined - Checks whether a given named constant exists

SYNOPSIS

       bool defined (string  $name)

DESCRIPTION

	Checks whether the given constant exists and is defined.

       Note

	       If  you	want  to  see if a variable exists, use isset(3) as defined(3) only applies to constants. If you want to see if a function
	      exists, use function_exists(3).

PARAMETERS

	      o $name
		- The constant name.

RETURN VALUES

	Returns TRUE if the named constant given by $name has been defined, FALSE otherwise.

EXAMPLES

       Example #1

	      Checking Constants

	      <?php
	      /* Note the use of quotes, this is important.  This example is checking
	       * if the string 'TEST' is the name of a constant named TEST */
	      if (defined('TEST')) {
		  echo TEST;
	      }
	      ?>

SEE ALSO

       define(3), constant(3), get_defined_constants(3), function_exists(3), The section on Constants.

PHP Documentation Group 														DEFINED(3)

Linux and UNIX Man Pages

function_exists(3) [php man page]

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