Detailed explanation of PHP function parameter passing

PHP is a language widely used in website backend development, and its function parameter passing is also one of its basic features, which is very important. This article will explain in detail the relevant knowledge of PHP function parameter passing.

1. Pass-by-value and pass-by-reference

In PHP function parameter passing, there are two ways: pass-by-value and pass-by-reference. Passing by value means copying the value of the actual parameter to the formal parameter. Modifications to the formal parameter within the function will not affect the actual parameter. Passing by reference passes the memory address of the actual parameter to the formal parameter. Modifications to the formal parameter within the function will also directly affect the actual parameter.

For example:

function addOne($a){
    $a++;
}

function addOneRef(&$a){
    $a++;
}

$num = 1;
addOne($num);
echo $num;   // 输出1，因为实参$num的值并未被修改

addOneRef($num);
echo $num;   // 输出2，因为实参$num的值被修改了

2. Passing multiple parameters

In PHP, you can specify multiple formal parameters when defining a function, and at the same time in the function The need to pass multiple parameters is achieved by passing multiple actual parameters when calling. It should be noted that actual and formal parameters correspond in order of position, so you need to pay attention to the order of parameters when passing parameters.

For example:

function calculate($a, $b, $c){
    return ($a + $b) * $c;
}

echo calculate(1, 2, 3);    // 输出9

3. Default parameters

Sometimes, when we define a function, we want the default value of some parameters to be a specific value, then Can be set using default parameters.

For example:

function welcome($name, $age = 18){
    echo "欢迎你，$name，你今年$age岁了！";
}

welcome("小明");   // 输出：欢迎你，小明，你今年18岁了！
welcome("小华", 20);   // 输出：欢迎你，小华，你今年20岁了！

4. Indefinite length parameters

In some cases, the number of parameters we may need to pass is uncertain. In this case, you can Use variable length parameters to solve this problem.

In PHP, you can use the two functions func_get_args() and func_num_args() to transfer and obtain variable-length parameters.

For example:

function sum(){
    $result = 0;
    $args = func_get_args(); // 获取所有不定长参数
    $count = func_num_args(); // 获取不定长参数的数量
    for ($i = 0; $i < $count; $i++){
        $result += $args[$i];
    }
    return $result;
}

echo sum(1, 2, 3, 4);   // 输出10

The above is the basic content of PHP function parameter passing. In actual applications, developers need to choose different parameter transfer methods based on actual needs, and rationally use features such as default parameters and variable-length parameters. At the same time, you need to pay attention to the reasonable use of pass-by-value and pass-by-reference to avoid unnecessary errors and potential performance problems.

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