Most Referenced Functions
  » google_pagerank()
  » preg_replace()
  » imagecreatefrompng()
  » site_pageranks()
  » imagepng()
  » imagedestroy()
  » imagestring()
  » imagecolorallocate()
  » htmlentities()
  » fopen()
  » preg_match()
  » header()
  » getimagesize()
  » htmlspecialchars()
  » ob_start()
  » session_start()
  » strstr()
  » ob_flush()
  » preg_match_all()
  » strpos()
  » flush()
  » setcookie()
  » str_replace()
  » array2vars()
  » nl2br()
  » preg_split()
  » ereg()
  » urlencode()
  » ereg_replace()
  » readgzfile()

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PHP Functions

Function: function_exists

(PHP 3 >= 3.0.7, PHP 4, PHP 5)

function_exists --  Return TRUE if the given function has been defined

Description

bool function_exists ( string function_name )

Checks the list of defined functions, both built-in (internal) and user-defined, for function_name . Returns TRUE on success or FALSE on failure.

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

Note that a function name may exist even if the function itself is unusable due to configuration or compiling options (with the image functions being an example). Also note that function_exists() will return FALSE for constructs, such as include_once() and echo() .

Related Function(s)

  • include_once()
  • echo()
  • method_exists()
  • get_defined_functions()
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