What is the difference betwen Variable in PHP4 and PHP5?

问题

the only thing i know about this subject is...

in PHP 5, when a variable used without assigned any value, then it a warning will be shown.

Is there any other difference between this 2 different version ?

回答1:

There is no general difference between variables in PHP 4 and 5.

What you are probably referring to is the ´E_NOTICE` error reporting level. When that level is turned on, PHP will complain if a variable is used that hasn't been assigned yet. That level existed in PHP 4 already:

// Report all errors except E_NOTICE
// This is the default value set in php.ini

error_reporting(E_ALL ^ E_NOTICE);

echo $hello_world;  // Will output nothing, but also not output a notice

error_reporting(E_ALL);

echo $hello_word;   // Will output "Notice: Undefined variable"

PHP's error reporting can be influenced through the "error_reporting" php.ini setting, or during runtime of the script using the error_reporting() function.

As for other differences, there's a load of them. Check out Gordon's link about Migrating from PHP 4 to 5.

回答2:

Actually, there is no real difference. An error being shown on use of undefined variables is a difference in PHP settings, not PHP version.

回答3:

There is not difference betwen variables in php4 and php5. You can stop error reporting by using this:

error_reporting('E_ALL ^ E_NOTICE'); 

来源：https://stackoverflow.com/questions/2487021/what-is-the-difference-betwen-variable-in-php4-and-php5