在php中按值调用和按引用调用之间的区别以及$$意味着什么? [英] difference between call by value and call by reference in php and also $$ means?

问题描述

(1)我想知道php中的按值调用和按引用调用之间的区别是什么. PHP可以按值调用还是按引用调用?

(1) I want to know what is the difference between call by value and call by reference in php. PHP works on call by value or call by reference?

(2)我也想知道您是通过$$登录php

(2) And also i want to know that do you mean by $$ sign in php

例如:-

$a = 'name';
$$a = "Paul";
echo $name; 

output is Paul

如上例所示，PHP上的$$是什么意思.

As above example what do u mean by $$ on PHP.

推荐答案

$$a = b;在PHP中的意思是取$a的值，并将其 name 值为该值的变量设置为等于b".

$$a = b; in PHP means "take the value of $a, and set the variable whose name is that value to equal b".

换句话说:

$foo = "bar";
$$foo = "baz";
echo $bar; // outputs 'baz'

但是，是的，请阅读 PHP符号参考.

对于按值/引用进行调用-两者之间的主要区别在于您是否能够修改用于调用该函数的原始项.参见:

As for call by value/reference - the primary difference between the two is whether or not you're able to modify the original items that were used to call the function. See:

function increment_value($y) {
    $y++;
    echo $y;
}

function increment_reference(&$y) {
    $y++;
    echo $y;
}

$x = 1;
increment_value($x); // prints '2'
echo $x; // prints '1'
increment_reference($x); // prints '2'
echo $x; // prints '2'

请注意，increment_value()不会更改$x的值，而increment_reference()会更改 .

Notice how the value of $x isn't changed by increment_value(), but is changed by increment_reference().

如此处所示，是使用按值调用还是按引用调用取决于被调用函数的定义.声明自己的函数时，默认值是按值调用(但您可以通过&标记指定按引用调用).

As demonstrated here, whether call-by-value or call-by-reference is used depends on the definition of the function being called; the default when declaring your own functions is call-by-value (but you can specify call-by-reference via the & sigil).

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