In PHP, how do I check if a function exists?

Question

How can I check if the function my_function already exists in PHP?

score 120 · Accepted Answer · answered Dec 04 '10 at 03:55

120

Using function_exists:

if(function_exists('my_function')){
    // my_function is defined
}

answered Dec 04 '10 at 03:55

Mark Elliot

75,278
22
140
160

18

And if you want to check for methods on classes, most people will recommend method_exists but that detects protected/private methods which aren't externally accessible. In that case is_callable is a better option in general. – CaseySoftware Dec 04 '10 at 04:27
3

@CaseySoftware - For convenience, [here's the doc](http://php.net/manual/en/function.is-callable.php) for ``is_callable``, as this answer was a top result on Google. – Andrew Cheong Sep 28 '12 at 08:37
2

It's hilarious how semantic and extensive PHP's library is. "how can I tell if a function exists?" "`function_exists`" – Ky - Aug 19 '15 at 17:34
how to check this function if exists? `$date = new DateTime(); $date->getTimestamp() ` ? – Disapamok Jun 13 '16 at 06:20
if(!function_exists('my_function')) { } – Gene Kelly Jan 02 '17 at 04:57

score 24 · Answer 2 · answered Jun 06 '13 at 12:28

24

http://php.net/manual/en/function.function-exists.php

<?php
  if (!function_exists('myfunction')) {

     function myfunction()
     {
       //write function statements
     }

}
 ?>

answered Jun 06 '13 at 12:28

Avinash Saini

1,203
11
10

T.Todua · Answer 3 · 2019-01-02T09:02:16.353

8

var_dump( get_defined_functions() );

DISPLAYS all existing functions

edited Jan 02 '19 at 09:02

answered Jan 28 '14 at 16:20

T.Todua

53,146
19
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237

score 3 · Answer 4 · answered Nov 08 '13 at 22:01

I want to point out what kitchin has pointed out on php.net:

<?php
// This will print "foo defined"
if (function_exists('foo')) {
  print "foo defined";
} else {
  print "foo not defined";
}
//note even though the function is defined here, it previously was told to have already existed
function foo() {}

If you want to prevent a fatal error and define a function only if it has not been defined, you need to do the following:

<?php
// This will print "defining bar" and will define the function bar
if (function_exists('bar')) {
  print "bar defined";
} else {
  print "defining bar";
  function bar() {}
}

score 3 · Answer 5 · answered Jul 08 '19 at 13:38

And if my_function is in namespace:

namespace MyProject;

function my_function() {
    return 123;
}

You can check if it exists

function_exists( __NAMESPACE__ . '\my_function' );

in the same namespace or

function_exists( '\MyProject\my_function' );

outside of the namespace.

P.S. I know this is a very old question and PHP documentation improved a lot since then, but I believe people still taking a peek here, and this might be helpful.

score 1 · Answer 6 · edited Jun 01 '19 at 11:50

Checking Multiple function_exists

$arrFun = array('fun1','fun2','fun3');
if(is_array($arrFun)){
  $arrMsg = array();
  foreach ($arrFun as $key => $value) {
    if(!function_exists($value)){
      $arrMsg[] = $value;
    }
  }
  foreach ($arrMsg as $key => $value) {
    echo "{$value} function does not exist <br/>";
  }
}
function fun1(){
}

Output

fun2 function does not exist 
fun3 function does not exist

In PHP, how do I check if a function exists?

6 Answers6

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