PHP get_defined_functions() Function: Usage and Examples

Use get_defined_functions() when you need to returns the functions currently defined in PHP in a PHP application. The examples below show the actual operation and its limitations.

What Is get_defined_functions() in PHP?

Returns the functions currently defined in PHP. The exact signature supported by your installation depends on its PHP version and enabled extensions.

Its syntax is:

get_defined_functions(bool $exclude_disabled = ...): array

Parameters and return value: The parameter types, optional arguments, references, and return type are shown in the signature above. Optional parameters are marked with an ellipsis in this reference signature.

Example 1: Basic Usage

<?php

$functions = get_defined_functions(); echo in_array("strlen", $functions["internal"], true) ? "Available" : "Missing";

Result: Run the example in an environment that supports the function. Any values depending on operating-system state, installed extensions, process configuration, or network access must be checked on the target server.

Example 2: Different Input or Behavior

<?php

$functions = get_defined_functions(); echo count($functions["internal"]) > 0 ? "Internal functions found" : "None";

Result: Run the example in an environment that supports the function. Any values depending on operating-system state, installed extensions, process configuration, or network access must be checked on the target server.

Practical Example: Applying the Function

<?php

$defined = get_defined_functions(); $matches = array_filter($defined["internal"], fn($name) => str_starts_with($name,"json_")); echo count($matches) . " JSON functions";

Result: Run the example in an environment that supports the function. Any values depending on operating-system state, installed extensions, process configuration, or network access must be checked on the target server.

Important Behavior and Edge Cases

Installed extensions affect the list; counts differ between systems.

Comparison With Related Functions

Common Beginner Mistakes

Key Takeaways

• Returns the functions currently defined in PHP.
• Installed extensions affect the list; counts differ between systems.
• function_exists() tests one function; get_defined_functions() enumerates functions.

Use get_defined_functions() for the specific operation demonstrated above. Check its prerequisites and handle failure conditions before using it with production data.