PHP 5.4忽略include中的define（）？

Question

Not sure if this is due to a module I have installed or not, I've tried to remove all the extensions I have but this still doesn't work:

//test1.php
if(defined("TEST1")) {
        return;
}
define("TEST1",1);
function test() {}

//test2.php
if(defined("TEST1")) {
        return;
}
define("TEST1",1);
function test() {}

//test.php
include_once('test1.php');
include_once('test2.php');
test();

Results in a duplicate definition error. It looks like other checks like function_exists will work, but it's a bit messier to use.

Answer 1

According to PHP documentation ( http://php.net/manual/en/functions.user-defined.php ):

Functions need not be defined before they are referenced, except when a function is conditionally defined

It means that if you don't put your test() function into conditional statement it will be defined BEFORE script execution start.

To allow referencing functions that are defined further in the code, PHP at first searches the file for function (classes, etc) definitions, then runs the code. So when you're doing your:

if(defined('TEST1')) return;

Te function already exists and dupplicate error is triggered. The solution is to put them in any conditional statement (it does not have to make sense) or even just in braces. Functions defined in that manner will not be defined before script execution and also you won't be able to use them befere they are defined. You can fix your code just by doing this:

//test1.php
if(defined("TEST1")) {
        return;
}
define("TEST1",1);

{
    function test() {}
}

//test2.php
if(defined("TEST1")) {
        return;
}
define("TEST1",1);

{
    function test() {}
}

//test.php
include_once('test1.php');
include_once('test2.php');

test();

To test the behavior you can play with that two code snippets. This one will work:

<?php

test();

function test() {
    echo 'Hello world!';
}

But this will fail with undefined function:

<?php

test();

{
    function test() {
        echo 'Hello world!';
    }
}

While this again will work:

<?php

{
    function test() {
        echo 'Hello world!';
    }
}

test();

Answer 2

Try

//test1.php
if(!defined("TEST1")) {
  define("TEST1",1);
  function test() {}
}

//test2.php
if(!defined("TEST1")) {
  define("TEST1",1);
  function test() {}
}

//test.php
include_once('test1.php');
include_once('test2.php');
test();