PHP致命错误取决于...浏览器类型？

Question

The situation described below caused a fatal error in PHP in about 50% of the browsers whereas in other browsers the code ran normally. No browser or any client info sniffing was used. As far as I know this should not be possible (PHP running differently depending on client browser). The issue has been resolved but I still want to understand exactly how this could happen.

So index.php includes 2 files:

include('a.php');
include('b.php');

a.php:

the_function();

b.php:

function the_function(){
  //code
}

The fatal error in 50% of the browsers was that the_function was not defined in a.php, so a.php was executed immediately upon include. Whereas in other browsers it seemed to first include all php files and only then start executing.

If I remember correctly they were Mac Safari, Mac Chrome, and IE but I don't even know whether this behavior is shared among the same browsers on different machines.

the issue of course was resolved by switching the order of includes. But I still want to understand why this happened.

Answer 1

Not 100% sure but as far as i know this behaviour can happen when the PHP code is cached in APC or another bytecode cache. For this reason sometimes the code is already cached and the function is available at beginning.

In PHP you can define the function later than calling it and it works, if you are in the same file. Example: https://3v4l.org/m951d

So, it not depends on the browsers, it depends on the current cache status for the php script.