How does PHP parse functions

Question

Well I confused by behavior of PHP when parsing a PHP file. I am reading this since long that

The PHP language is interpreted

So I have code

var_dump(function_exists('abc')); exit;
function abc() {
    return;
}

var_dump should print false as per my assumption but it print bool(true).

Can somebody please help me to understand this behavior?

it's pre-compiled before running, not interpreted while running AFAIK — RST
– RST, Commented Jan 7, 2016 at 8:00
function abc() was called before exit; (using function_exists) that's why it returns 'true'. Even if you define the function after exit and it is called before exit, it still execute. — Ren Camp
– Ren Camp, Commented Jan 7, 2016 at 8:02
what I meant was, using function_exists(), the function abc() was called because it searched if that certain function exists. — Ren Camp
– Ren Camp, Commented Jan 7, 2016 at 8:04
What you see here is often called "function hoisting". Non-conditional definitions of functions are "hoisted" to the top of the script. — NikiC
– NikiC, Commented Jan 8, 2016 at 14:12

Community · Accepted Answer · 2017-05-23 12:33:21Z

2

See this answer.

In short, it is compiled into a type of bytecode at runtime and then interpreted - in doing this, you will have the definitions for your functions available, even if they appear at the very end.

edited May 23, 2017 at 12:33

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answered Jan 7, 2016 at 8:12

Matt Clark

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3 Comments

Sumit Over a year ago

Okay so finally PHP is not just interpreted as people say?

Matt Clark Over a year ago

Well it is, but the code has to be turned into something readable by the interpreter, this bytecodeish form has your code optomized for the interpreter.

Sumit Over a year ago

Well it make sense. Thanks Matt.

Drudge Rajen · Accepted Answer · 2016-01-07 08:23:38Z

0

function_exist will Checks the list of defined functions, both built-in (internal) and user-defined, for function_name. So, php interpreter checks if the function with the name is defined in the bytecode which is complied before interpreted.

answered Jan 7, 2016 at 8:23

Drudge Rajen

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