PHP变量是按值传递还是按引用传递?


当前回答

关于如何将对象传递给函数,你仍然需要理解,没有“&”,你传递给函数的是一个对象句柄,对象句柄仍然是通过值传递的,它包含一个指针的值。但你不能改变这个指针,直到你通过引用传递它使用“&”

<?php
        class Example 
        {
            public $value;
         
        }
        
        function test1($x) 
        {
             //let's say $x is 0x34313131
             $x->value = 1;  //will reflect outsite of this function
                             //php use pointer 0x34313131 and search for the 
                             //address of 'value' and change it to 1

        }
        
        function test2($x) 
        {
             //$x is 0x34313131
             $x = new Example;
             //now $x is 0x88888888
             //this will NOT reflect outside of this function 
             //you need to rewrite it as "test2(&$x)"
             $x->value = 1000; //this is 1000 JUST inside this function
                 
        
        }
         
     $example = new Example;
    
     $example->value = 0;
    
     test1($example); // $example->value changed to  1
    
     test2($example); // $example did NOT changed to a new object 
                      // $example->value is still 1
     
 ?>

其他回答

关于如何将对象传递给函数,你仍然需要理解,没有“&”,你传递给函数的是一个对象句柄,对象句柄仍然是通过值传递的,它包含一个指针的值。但你不能改变这个指针,直到你通过引用传递它使用“&”

<?php
        class Example 
        {
            public $value;
         
        }
        
        function test1($x) 
        {
             //let's say $x is 0x34313131
             $x->value = 1;  //will reflect outsite of this function
                             //php use pointer 0x34313131 and search for the 
                             //address of 'value' and change it to 1

        }
        
        function test2($x) 
        {
             //$x is 0x34313131
             $x = new Example;
             //now $x is 0x88888888
             //this will NOT reflect outside of this function 
             //you need to rewrite it as "test2(&$x)"
             $x->value = 1000; //this is 1000 JUST inside this function
                 
        
        }
         
     $example = new Example;
    
     $example->value = 0;
    
     test1($example); // $example->value changed to  1
    
     test2($example); // $example did NOT changed to a new object 
                      // $example->value is still 1
     
 ?>

取决于版本,4是值,5是引用。

两种方法都可以。

在前面放一个“&”符号,你传递的变量就变成了它的原点,也就是说,你可以通过引用传递,而不是复制它。

so

    $fred = 5;
    $larry = & $fred;
    $larry = 8;
    echo $fred;//this will output 8, as larry and fred are now the same reference.

可以通过引用将变量传递给函数。这个函数将能够修改原始变量。

你可以在函数定义中通过引用来定义段落:

<?php
function changeValue(&$var)
{
    $var++;
}

$result=5;
changeValue($result);

echo $result; // $result is 6 here
?>

在PHP 5中通过引用传递对象,在PHP 4中通过值传递对象。 默认情况下,变量是按值传递的!

阅读此处:http://www.webeks.net/programming/php/ampersand-operator-used-for-assigning-reference.html