header() error not shown in php

Question

I wrote a PHP program, I use session_start() and header() functions, I know I should use this functions before I sending anything to client. it\'s ok,

Answer 1

I found the problem, I don't use any FrameWork.

the problem was error_reporting('E_ALL');

I wrote this code on first of my program, and so PHP didn't return any errors ! I deleted this line and I get the errors !

This is kidding because this line said to PHP to show ALL errors ! I don't know why PHP don't show any errors.