php validate exist

function_exists — Return TRUE if the given function has been defined.
(PHP 4, PHP 5)

method_exists() - Checks if the class method exists.
is_callable() - Verify that the contents of a variable can be called as a function.
get_defined_functions() - Returns an array of all defined functions.
class_exists() - Checks if the class has been defined.
extension_loaded() - Find out whether an extension is loaded.
defined - an inbuilt function in PHP which checks whether a constant is exists or not, in other words, defined or not.

Similar topic:

Variable handling Functions

PHP Class Function Validate

PHP function Variable Checking / Validate

php validate exist

Inspiration:
https://geeksforgeeks.org/