What is the difference between passing by value and pas…

In PHP, passing by value and passing by reference are two different ways of passing parameters.

When passing parameters by value, a function creates a copy of the parameter and then passes the copy to the function. Any modifications to the parameter inside the function will not affect the original variable.

For example:

function increment($num) {
    $num++;
}

$number = 5;
increment($number);
echo $number; // 输出 5

In the example above, despite incrementing $num inside the function, this will not affect the original $number variable.

On the contrary, when passing parameters by reference, the function receives a reference to the original variable and can directly modify the original variable.

For example:

function increment(&$num) {
    $num++;
}

$number = 5;
increment($number);
echo $number; // 输出 6

In the example above, by adding the & symbol before the parameter, the parameter is set to be passed by reference. This means that incrementing $num inside the function will directly affect the original $number variable.

In summary, when passing parameters by value, functions make a copy of the parameter and do not affect the original variable. When passing parameters by reference, functions receive a reference to the original variable and can directly modify it.