Detailed explanation of passing by value and passing by address (reference) in PHP functions_PHP Tutorial

In PHP, it is relatively simple for us to pass values ​​by function, but some naive friends may not understand function passing by address or reference. The following editor will introduce to you the function passing by value and address (reference) in PHP. ) introduction, I hope it will be helpful to you.

Usage quoted in php:

1. Reference assignment of variables: $a = &$b

2. Passing reference parameters when calling functions

1) In early PHP, reference type variables were passed through the & symbol when calling, such as: func(&$arg);

2) Later, the reference type parameters of the function were stipulated to need to be defined when the function was declared, instead of: function func(&$arg);

Note: After defining reference type parameters during reference declaration, runtime reference parameter passing is abandoned. You need to add allow_call_time_pass_reference to php.ini to enable it.

3. The function returns a reference type. This application method requires adding an & symbol before the function name when declaring the function, and when calling, use the reference assignment method, such as:

The code is as follows

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代码如下	复制代码
function &func() {     return $a; } $a = func();  //这种调用方式得到的不是引用传值 $a =& func(); //这样调用才是引用传值

function &func() {
Return $a;
}
$a = func(); //This method of calling does not result in pass-by-reference
$a =& func(); //This is a call by reference

In short, it is to let the function return a reference type value. A more practical example:

代码如下	复制代码
$a = 1; function &func(&$a) {   return $a; } $b = func($a); $c =& func($a); $b = 2; echo "a: $a, b: $b, c: $c. /n"; //输出a: 1, b: 2, c: 1. //可见对$b的修改不会影响$a $c = 3; echo "a: $a, b: $b, c: $c. /n"; //输出a: 3, b: 2, c: 3. //可见对$c的修改会影响$a

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$a = 1; function &func(&$a) { return $a; } $b = func($a); $c =& func($a); $b = 2; echo "a: $a, b: $b, c: $c. /n"; //Output a: 1, b: 2, c: 1. //It can be seen that the modification of $b will not affect $a $c = 3; echo "a: $a, b: $b, c: $c. /n"; //Output a: 3, b: 2, c: 3. //It can be seen that the modification of $c will affect $a

Several details of value transfer in php function

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//1. Value passing of basic data types

代码如下

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//一、基本数据类型的传值   /* **************************************************** */  function testvar($k){  $k = 40; } $c = 30; //给一个函数参数传一个基本数据类型(整型，布尔，字符 ...)， 实际上传的就是值 ; testvar($c); echo $c;//结果是：30     function testvar2(&$k){  $k = 40; } $e = 30; //给一个函数参数传一个基本数据类型(整型，布尔，字符 ...)， 实际上传的y就是地址 ; testvar2($e); echo $e;//结果是：40   /* **************************************************** */ //二、数组（默认情况下是复制一份数据），如要传地址则&$arr. $arr1 = array(-1,5,0); function testArr($arr){  for($i=0;$i for($j=$i+1;$j if($arr[$i]>$arr[$j]){     $temp = $arr[$i];     $arr[$i] = $arr[$j];     $arr[$j] = $temp;    }   }    }  print_r($arr);  //结果:Array ( [0] => -1 [1] => 0 [2] => 5 ) } testArr($arr1); print_r($arr1);  //结果:Array ( [0] => -1 [1] => 5 [2] => 0 )   function testArr2(&$arr){  for($i=0;$i for($j=$i+1;$j if($arr[$i]>$arr[$j]){     $temp = $arr[$i];     $arr[$i] = $arr[$j];     $arr[$j] = $temp;    }   }    } } testArr($arr1); print_r($arr1);  //结果:Array ( [0] => -1 [1] => 0 [2] => 5 )         /* **************************************************** */ //三、对象数据类型传值 class person{  public $name;  public  $age; }   $a = new person(); $a->name = '小明'; $a->age = '20'; //变量a在存的是对象的地址，把a赋给b这个变量，实际上就是赋了一个地址。 $b = $a; $b->age = 30; //echo $a->age.$b->age;//结果是：30 30 //给一个函数参数传一个对象， 实际上传的是这个对象的地址; function test($k){  $k->age =40; } //调用 test($b); //echo $a->age.$b->age;//结果是：40 40

/************************************************* **** */ function testvar($k){ $k = 40; } $c = 30; //Pass a basic data type (integer, Boolean, character...) to a function parameter, and what is actually passed is the value; testvar($c); echo $c;//The result is: 30 function testvar2(&$k){ $k = 40; } $e = 30; //Pass a basic data type (integer, Boolean, character...) to a function parameter. In fact, the y passed is the address; testvar2($e); echo $e;//The result is: 40 /************************************************* **** */ //2. Array (by default, a copy of the data is copied). If you want to pass the address, then &$arr. $arr1 = array(-1,5,0); function testArr($arr){ for($i=0;$i for($j=$i+1;$j if($arr[$i]>$arr[$j]){ $temp = $arr[$i]; $arr[$i] = $arr[$j]; $arr[$j] = $temp; } } } print_r($arr); //Result:Array ( [0] => -1 [1] => 0 [2] => 5 ) } testArr($arr1); print_r($arr1); //Result:Array ( [0] => -1 [1] => 5 [2] => 0 ) function testArr2(&$arr){ for($i=0;$i for($j=$i+1;$j if($arr[$i]>$arr[$j]){ $temp = $arr[$i]; $arr[$i] = $arr[$j]; $arr[$j] = $temp; } } } } testArr($arr1); print_r($arr1); //Result:Array ( [0] => -1 [1] => 0 [2] => 5 ) /************************************************* **** */ //3. Pass value of object data type class person{ public $name; public $age; } $a = new person(); $a->name = 'Xiao Ming'; $a->age = '20'; //The variable a stores is the address of the object. Assigning a to the variable b actually assigns an address. $b = $a; $b->age = 30; //echo $a->age.$b->age;//The result is: 30 30 //Pass an object to a function parameter. What is actually passed is the address of the object; function test($k){ $k->age =40; } //Call test($b); //echo $a->age.$b->age;//The result is: 40 40

What is the difference between passing by value and passing by address in PHP function? I like to get answers to questions like this through program demonstrations. Let’s take a look at a demo recording!

代码如下	复制代码
$i=100; function func($n){ $n=$n+100; return $n; } echo '1)函数传值前变量$i的值:'.$i.' ';    echo '2)传值后函数的返回值:'.func($i).' ';    echo '3)函数传值后变量$i的值:'.$i.' ';    echo '4)函数传址前变量$i的值:'.$i.' ';    echo '5)传址后函数的返回值:'.func(&$i).' ';    echo '6)函数传址后变量$i的值:'.$i.' ';    //echo func($i).' ';    ?>

Program output:

1) The value of variable $i before the function passes the value: 100
2) The return value of the function after passing the value: 200
3) The value of variable $i after the function passes the value: 100
4) The value of variable $i before function transfer: 100
5) The return value of the function after passing the address: 200
6) The value of variable $i after function transfer: 200
 
Explanation:

1) Directly output a variable assigned $i=100
2) The func function passes a value and returns an arithmetic addition result $=100+100
3) When the func function passes a value, its scope of action is limited to the inside of the function and will not affect the external variable $i
4) Same as above
5) There is an additional "&" character before the func function parameter, indicating address transfer. Like 2), the return value is the arithmetic operation result of the function.

6) func(&$i), the variable pointer points to the position of $i, which can be understood as an operation on the variable $i, $i=$i+100; at this time, the variable $i has been equivalent to being reassigned

What will be the result if you remove the comment on line 18 of the above code?

Summary: Passing by address is to change the function parameter value while executing the function, but passing by value is not expected to change.

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