What is the difference between php4 and php5

The difference between php4 and php5: 1. There is no destructor in php4, but there is a destructor in php5; 2. When passing a variable to a function or method in php4, the variable is actually copied once , and objects in php5 always exist in the form of references.

The operating environment of this tutorial: windows10 system, PHP7.1 version, DELL G3 computer

What is the difference between php4 and php5

Constructor and destructor

In PHP4, when a function has the same name as an object, this function will become the constructor of the object, and there is no concept of a destructor in PHP4.

In PHP5, the constructor is uniformly named __construct, and the concept of destructor is introduced, which is uniformly named __destruct.

Example 1: Constructor and Destructor

class foo {undefined
var $x;
function __construct($x) {undefined
$this->x = $x;
}
function display() {undefined
print($this->x);
}
function __destruct() {undefined
print("bye bye");
}
}
$o1 = new foo(4);
$o1->display();
?>

In the above example, when you terminate the call to the foo class, its destructor will be called. In the above example, Output "bye bye".

Object reference

As we all know, in PHP4, passing a variable to a function or method actually copies the variable, which means that the variable you pass to the function or method is copied. Is a copy of this variable, unless you use the reference symbol "&" to declare that you want to make a reference, not a copy. In PHP5, objects always exist in the form of references, and assignment operations in objects are also reference operations.

Example 2: Reference of object

class foo {undefined
var $x;
function setX($x) {undefined
$this->x = $x;
}
function getX() {undefined
return $this->x;
}
}
$o1 = new foo;
$o1->setX(4);
$o2 = $o1;
$o1->setX(5);
if($o1->getX() == $o2->getX()) print("Oh my god!");
?>

Clone of object

As mentioned above, when an object is always called in the form of a reference, if I want to get the object What should I do with a copy of it? PHP5 provides a new feature, which is object cloning, with the syntax __clone.

Example 3: Object cloning

class foo {undefined
var $x;
function setX($x) {undefined
$this->x = $x;
}
function getX() {undefined
return $this->x;
}
}
$o1 = new foo;
$o1->setX(4);
$o2 = $o1->__clone();
$o1->setX(5); if($o1->getX() != $o2->getX()) print("Copies are independant");
?>

The method of object cloning exists in many other application languages, so you don’t have to worry about its stability. :)

Private, public and protected modes in objects

In PHP4, all methods and variables of an object are public, which means that you can operate on it outside of an object any variable and method. PHP5 introduces three new modes for controlling this access permission: Public, Protected, and Private.

• Public mode (Public): allows operation control outside the object.

• Private mode (Private): Only methods within this object are allowed to operate and control it.

• Protected mode (Protected): Allows this object and its parent object to operate and control it.

Recommended learning: "PHP Video Tutorial"

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