Function_exists to check if function is available or not in PHP

We can check built in function or user defined functions before using them. The built in function function_exists checks this and returns true of false. It takes one string input and returns Boolean output. Here is an example.

if(function_exists(is_int)){
echo " Yes this function is available to use ";
}else{
echo " Sorry , this is not available to use " ;
}

In the above code we have used is_int() which is a built in function in PHP, so we will get the output as this.

Yes this function is available to use

User defined functions

<?Php
function my_function($var1,$var2,$var3){
$var=$var1+$var2+$var3;
return $var;
}
echo my_function(5,6,8); // Output 19 

if(function_exists(is_int)){
echo " <br>Yes <i>my_function</i> is available to use ";
}else{
echo " <br>Sorry , <i>my_function</i> is not available to use " ;
}
?>

Output

19
Yes my_function is available to use

Example of uses

To check mysqli support, function_exists() is used.

if (function_exists('mysqli_connect')) {
  echo "mysqli is installed";
}else{
echo " Enable Mysqli support in your PHP installation "; 
}

Example: Checking Custom Function

function myFunction() {
    echo "Function exists!";
}
if (function_exists('myFunction')) {
    myFunction();  // Output: Function exists!
} else {
    echo "Function not found!";
}

Example: Preventing Fatal Errors

if (function_exists('nonexistentFunction')) {
    nonexistentFunction();  // Avoids fatal error
} else {
    echo "Function does not exist!";
}

### Description:
Custom Functions: Ensures that the custom function exists before executing it. Fatal Error Prevention: Prevents runtime fatal errors by checking the function's existence. Namespaces: When working with namespaces, ensure the function exists in the correct scope. ### Example: Working with Namespaces

namespace MyNamespace;

function customFunc() {
    echo "Namespace Function";
}

if (function_exists('MyNamespace\\customFunc')) {
    customFunc();  // Output: Namespace Function
}

This way, the `function_exists()` page can be improved by providing more real-life examples and handling different PHP contexts such as namespaces and custom functions.
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