Although most existing PHP 4 code should work without changes, you should pay attention to the following backward incompatible changes:
Example#1 strrpos() and strripos() now use the entire string as a needle
<?php
var_dump(strrpos('ABCDEF','DEF')); //int(3)
var_dump(strrpos('ABCDEF','DAF')); //bool(false)
?>
Example#2 An object with no properties is no longer considered "empty"
<?php
class test { }
$t = new test();
var_dump(empty($t)); // echo bool(false)
if ($t) {
// Will be executed
}
?>
Example#3 In some cases classes must be declared before used
<?php
//works with no errors:
$a = new a();
class a {
}
//throws an error:
$a = new b();
interface c{
}
class b implements c {
}
?>