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function_exists — Determines whether a function is defined.


boolean function_exists(function_name);
string function_name:


TRUE if the function exists; FALSE otherwise


function_exists() is used to determine whether the given function is defined in the current PHP environment.


PHP Version: 3.0.7+, 4+

See also

To find out whether a given method or class is defined:




Example 384. Find out whether a function exists

$function_name = 'get_big_raise';

if (function_exists ($function_name))
    print "Function <tt>$function_name</tt> exists (and there was much rejoicing).";
    print "Function <tt>$function_name</tt> does not exist.";

PHP Functions Essential Reference. Copyright © 2002 by New Riders Publishing (Authors: Zak Greant, Graeme Merrall, Torben Wilson, Brett Michlitsch). This material may be distributed only subject to the terms and conditions set forth in the Open Publication License, v1.0 or later (the latest version is presently available at The authors of this book have elected not to choose any options under the OPL. This online book was obtained from and is designed to provide information about the PHP programming language, focusing on PHP version 4.0.4 for the most part. The information is provided on an as-is basis, and no warranty or fitness is implied. All persons and entities shall have neither liability nor responsibility to any person or entity with respect to any loss or damage arising from the information contained in this book.

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