How to call a function in PHP

In PHP programming, functions are one of the very important components. A function is a block of code that can be called multiple times to perform a specific task. In addition to improving code reusability and maintainability, using functions can also simplify code and improve development efficiency. This article will introduce how to call functions in PHP.

1. Built-in functions

The PHP language has many commonly used functions built-in, such as string functions, time functions, file system functions, etc. To call a built-in function, just use the function name. Here are some examples of built-in functions:

// 字符串函数
$text = "hello world";
echo strlen($text); // 输出 11
echo strtoupper($text); // 输出 HELLO WORLD

// 时间函数
echo date("Y-m-d H:i:s"); // 输出当前时间

// 文件系统函数
$file = fopen("test.txt", "r");
echo fread($file, filesize("test.txt"));
fclose($file);

2. Custom functions

Custom functions are functions written according to the specific needs of developers. It can be called anywhere in the program, improving code reusability and reducing code redundancy. To define a custom function in PHP, you need to use the function keyword. The following is a simple example of a custom function:

function add($a, $b) {
  return $a + $b;
}
echo add(1, 2); // 输出 3

3. Anonymous function

Anonymous function is a function without a function name, also known as a closure function. Usually anonymous functions are used in scenarios where one-time functions need to be defined, such as callback functions and event handlers. To define an anonymous function in PHP, you need to use the function keyword and closing brackets (), and the function body needs to be wrapped in curly braces. The following is an example of an anonymous function:

$greet = function($name) {
  echo "Hello, {$name}!";
};
$greet("World"); // 输出 Hello, World!

4. Function call

To call a function in PHP, you need to use the function name and a pair of parentheses() , actual parameters can be passed to the function. The following is an example of calling a function:

// 调用内置函数
echo strlen("hello"); // 输出 5

// 调用自定义函数
function add($a, $b) {
  return $a + $b;
}
echo add(1, 2); // 输出 3

// 调用匿名函数
$greet = function($name) {
  echo "Hello, {$name}!";
};
$greet("PHP"); // 输出 Hello, PHP!

When calling a function, you can pass parameters, separated by commas. PHP also supports default parameter values ​​and variable number of parameters. Here are some examples of different parameter types:

// 默认参数值
function greet($name = "World") {
  echo "Hello, {$name}!";
}
greet(); // 输出 Hello, World!
greet("PHP"); // 输出 Hello, PHP!

// 可变数量的参数
function add(...$numbers) {
  $sum = 0;
  foreach ($numbers as $number) {
    $sum += $number;
  }
  return $sum;
}
echo add(1, 2, 3, 4); // 输出 10

5. Function return value

A function can return a value or an array, using return# at the end of the function ## keyword can return the value. The following is an example of a function return value:

// 返回一个值
function add($a, $b) {
  return $a + $b;
}
echo add(1, 2); // 输出 3

// 返回一个数组
function divide($a, $b) {
  return ["quotient" => $a / $b, "remainder" => $a % $b];
}
$result = divide(7, 3);
echo $result["quotient"];     // 输出 2
echo $result["remainder"];   // 输出 1

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