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PHP | function_exists() Function

Last Updated : 14 Mar, 2018

The function_exists() is an inbuilt function in PHP. The function_exists() function is useful in case if we want to check whether a function() exists or not in the PHP script. It is used to check for both built-in functions as well as user-defined functions.

Syntax:

boolean function_exists($function_name)

Parameter: This function accepts a single parameter $function_name. This is the name of function that we want to search in the list of defined function. This is a string type parameter.

Return Values: This function returns a Boolean value. In case a function with the name $function_name exists it returns TRUE, otherwise it returns FALSE. This function will also return FALSE for constructs like “include_once”, “echo” etc.

Below programs illustrate the function_exists() function in PHP:

Program 1:

<?php 
// PHP program to illustrate function_exists() 
  
// checking if the in_array() built-in function  
// exists or not 
if (function_exists('in_array'))  
{ 
    echo "in_array() function is available.\n"; 
}  
else
{ 
    echo "in_array() function is not available.\n"; 
} 
  
?> 

Output:

in_array() function is available.

Program 2:

<?php 
// PHP program to illustrate function_exists() 
  
// declaring a function named WelcomeMsg 
function WelcomeMsg() 
{ 
    echo "Welcome to GeeksforGeeks"; 
} 
  
// checking if the function named WelcomeMsg 
// exists or not 
if (function_exists('WelcomeMsg'))  
{ 
    echo "WelcomeMsg() function is available.\n"; 
}  
else
{ 
    echo "WelcomeMsg() function is not available.\n"; 
} 
  
?> 

Output:

WelcomeMsg() function is available.

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

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