Detailed explanation of the use of reference symbol (&) in php

The reference of php is to add the ampersand in front of the variable, function, object, etc. The reference in PHP means: different names access the same variable content. Here is how to use the reference of PHP. Friends who need it can refer to it. There is a difference between

and pointers in C language. The pointer in C language stores a reference to the address variable where the content of the variable is stored in memory.

PHP’s reference allows you to use two variables to point to the same content

$a="ABC"; 
$b =&$a; 
echo $a;//这里输出:ABC 
echo $b;//这里输出:ABC 
$b="EFG"; 
echo $a;//这里$a的值变为EFG 所以输出EFG 
echo $b;//这里输出EFG

Function call by address

I won’t go into details about the call by address. The code will be given directly below

<?php
function test(&$a) {
  $a = $a + 100;
}
$b = 1;
echo $b; //输出１
test($b); //这里$b传递给函数的其实是$b的变量内容所处的内存地址，通过在函数里改变$a的值　就可以改变$b的值了
echo "<br>";
echo $b; //输出101

?>

It should be noted that if test(1); is used here, an error will occur. Think about the reason yourself.

The reference return of the function

Look at the code first

<?php
function &test() {
  static $b = 0; //申明一个静态变量
  $b = $b + 1;
  echo $b;
  return $b;
}
$a = test(); //这条语句会输出　$b的值　为１
$a = 5;
$a = test(); //这条语句会输出　$b的值　为2
$a = & test(); //这条语句会输出　$b的值　为3
$a = 5;
$a = test(); //这条语句会输出　$b的值　为6

?>

The following explanation:

In this way, $a=test(); is not actually returned by a reference to the function, which is different from ordinary There is no difference in function calls. As for the reason: This is the regulation of PHP.
PHP stipulates that the reference return of the function is obtained through $a=&test();.
As for what is a reference return (the PHP manual says: Reference return is used when you want to use a function to find which variable the reference should be bound to.) This nonsense made me unable to understand it for a long time

Use the above example to explain it

Calling a function with $a=test() only assigns the value of the function to $a, and any changes to $a will not affect $b in the function. Through $a=&test () method calls a function, its function is to point the memory address of the $b variable in return $b and the memory address of the $a variable to the same place, which produces the equivalent of this effect ($a=&b; ) So changing the value of $a also changes the value of $b, so after executing

##$a=&test(); $a=5
;

<?php
class a {
  var $abc = "ABC";
}
$b = new a;
$c = $b;
echo $b->abc; //这里输出ABC
echo $c->abc; //这里输出ABC
$b->abc = "DEF";
echo $c->abc; //这里输出DEF

?>

The default in PHP5 is to call objects by reference, but sometimes you may want to Create a copy of an object and hope that changes to the original object will not affect the copy. For this purpose, PHP defines a special method called __clone.

quoted Function

Unreference

$a = 1; 
$b =& $a; 
unset ($a);

global reference

$var =& $GLOBALS["var"];

$this

$a="ABC"; 
$b=$a;

$a="EFG";

PHPThe benefit of joining a namespace is to facilitate automatic loading

PHPError level setting and principle analysis

php process control break statement

continue statement for php process control

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