PHP/Functions/function exists
bool function_exists ( string function_name ) returns true if that function is available for use.
<source lang="html4strict">
<?
if (function_exists("imagepng")) {
echo "You have the GD extension loaded.";
} else {
echo "Can"t find imagepng( ) - do you have GD loaded?";
}
?>
</source>
Testing for a Function"s Existence
<source lang="html4strict">
<html> <body>
<?php
function tagWrap( $tag, $txt, $func="" ) {
if ( function_exists( $func ) )
$txt = $func( $txt );
return "<$tag>$txt</$tag>\n";
}
function subscript( $txt ) {
return "$txt";
}
print tagWrap("b", "bold");
print tagWrap("i", "i", "subscript");
?>
</body> </html>
</source>
