PHP | function_exists() Function

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
// 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
// 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