How to customize functions in PHP

In PHP, a function is a set of reusable blocks of code that are identified by a name. PHP supports a large number of ready-made functions, such as array_push, explode, etc., but sometimes you need to write your own functions to implement specific functions or improve code reusability. In this article, I will introduce how to customize functions in PHP, including function declaration, calling and using function parameters.

1. Declaration of function

To declare a function in PHP, you need to use the keyword function. The basic syntax of the function is as follows:

function function_name($arg1, $arg2, ...) {
  // 代码块
  return $result; // 可选的返回值
}

Among them, function_name is the name of the function, $arg1, $arg2,... are the parameter list of the function, and the return type does not need to be specified.

2. Call a custom function

After declaring the custom function, we can call the custom function just like calling the built-in function. The syntax is as follows:

$result = function_name($arg1, $arg2, ...);

Among them, $arg1, $arg2,... are the parameter list of the function.

3. Using function parameters

Function parameters are an important factor in making functions more useful. Inside the function, we can manipulate different data through the parameters passed to the function.

Function parameters in PHP are divided into two types: value parameters and reference parameters. When using value parameters, the function copies the value of the parameter when called and saves it inside the function. When using reference parameters, the function uses the variable itself that is passed to it, rather than a copy of the variable. This allows the function to modify the value of the variable when called.

The following are two examples of using different parameter types:

// 值参数
function add($a, $b) {
  $result = $a + $b;
  return $result;
}

$result = add(1, 2); // 3

// 引用参数
function add_one(&$a) {
  $a += 1;
}

$num = 1;
add_one($num); // $num 变为 2

In this example, the add function uses two value parameters. When we call this function, $a and $b are initialized to 1 and 2, and the result is returned by summing.

Another function add_one uses a reference parameter. When calling this function, we pass a reference to the variable $num, and its value is modified to 2.

4. Conclusion

Custom functions are an effective way to write reusable code. In PHP, function declaration is the basic syntax using the function keyword. To use functions, just call them like built-in functions. Finally, we can make functions more useful by passing parameters and consider using reference parameters to change the value of variables.

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