Example of PHP Reference & Usage

A reference to PHP is to precede variables or functions, objects, etc. with & symbols. The reference in PHP means: Different names access the same variable content. There is a difference between pointers in C and C, where the contents of a variable are stored in memory.

A reference to a variable

PHP references allow you to use two variables to point to the same content.

Invocation of a function's address

Address call I will not say more, the following direct code:

Function test (& $a) {$a = $a +100;} $b = 1; echo $b;//Output 1test ($b);   

It is important to note that here Test (1), the words will be wrong, reason to think.

A reference to the function returns

Look at the code first:

In this way $a=test () is not actually returned by a function reference, which is not the same as a normal function call. As for the reason: this is the PHP rule. PHP rules through $a=&test (); The way to get is to return the reference to the function. As for what is a reference return (the PHP manual says that reference return is used when you want to use a function to find out which variable the reference should be bound to.) ）

This is explained by the example above:

$a =test () call the function, just assign the value of the function to $ A, and no change to $ A will affect the $b in the function. by $a=&test (), the function is to call the memory address of the $b variable in the return $b and the memory address of the $ A variable to point to the same place, which produces the equivalent effect ($a =&b;) So changing the value of $ A also changes the value of the $b, so it executes the

Later, the value of the $b becomes 5.

This is to let everyone understand that the function reference returns only use static variables, in fact, the function of the reference return is used in the object.

References to Objects

The replication of objects in PHP5 is done by reference. The above $b=new A; $c = $b; is actually equivalent to $b=new A; $c =& $b; The default in PHP5 is to invoke the object by reference, but sometimes you might want to make a copy of the object, and you want the original object to change without affecting the copy. For this purpose, PHP defines a special method called __clone.

The role of the reference: if the program is relatively large, referencing the same object is more variable, and you want to use the object after the manual removal of it, the individual suggested the "&" method, and then $var=null to clear. At other times, it's the default way to use PHP5. In addition, in the PHP5 for large arrays of delivery, it is recommended to use "&" mode, after all, saving memory space to use.

When you unset a reference, you just break the binding between the variable name and the variable content. This does not mean that the contents of the variable are destroyed. For example:

<?php $a = 1; $b =& $a; unset ($a);?>  

Not unset $b, just $a.

When you declare a variable with the global $var, you actually establish a reference to the global variable. In other words, it is the same as doing this:

<?php $var =& $GLOBALS ["var"];?>  

This means, for example, that the unset $var does not unset global variables.

$this in the method of an object, $this is always a reference to the object that called it.

PHP in the direction of the address (similar to the pointer) function is not implemented by the user itself, is implemented by the Zend Core, PHP refers to the use of "copy-on-write" principle, that is, unless a write operation, the same address to the variable or object is not copied.

In layman's words, if you have the following code:

In fact, $ A and $b both point to the same memory address, not $ A and $b occupy different memory.

If you add the following code based on the above code:

$a = "EFG";

Since $ A and $b point to the memory of the data to be re-written once, at this time the Zend core will automatically decide to automatically produce a $ A copy of the data for $b, re-request a piece of memory for storage.

!!! http://www.nowamagic.net/librarys/veda/detail/851

Example of PHP Reference & Usage