How to declare php custom function

In real projects, when the PHP function cannot meet our needs, we can write our own function to complete any task. This is a custom function. In the previous article, we explained the concept of custom functions in detail and introduced What is a PHP custom function? How to declare PHP custom functions? Let’s learn about the basic structure of PHP custom functions.

To declare a custom function in php, you can use the following syntax format:

<?php
function 函数名（参数1,参数2,....）  //函数头
{
   函数体;                 //任何有效的php代码都可以作为函数体使用
   return 返回值;            //可以从函数中返回一个值
}
?>

Explanation of the syntax format of the function:

(1) The first character of each function Each line is a function header, which consists of three parts: the keyword function declaring the function, the function name, and the parameter list. Each part completes a specific function.

(2) Each custom function must be declared using the "function" keyword.

(3) The function name can represent the entire function, and the function can be named any name, as long as it follows the naming rules of variable names. Each function has a unique name, but it should be noted that function overloading cannot be used in PHP, so functions with the same name cannot be defined, including functions that cannot have the same name as system functions. Assigning a name to a function that describes its function is a common practice in development.

(4) When declaring a function, the brackets after the function name are also necessary. The brackets indicate a set of acceptable parameter lists. The parameters are the declared variables, and then some values ​​are passed to it when the function is called. . The parameter list can be absent or not written, or it can contain one or more parameters. Multiple parameters need to be separated by commas.

(5) The function body is located after the function header, enclosed in curly braces. The actual work is done in the function body. After the function is called, the first statement in the function body is executed first, and execution ends after the return statement or the outermost curly brace, and returns to the calling program. Any valid PHP code can be used in the function body, and even other function or class definitions can be declared in the function body.

(6) Use the keyword return to return a value from the function. Add an expression after return. When the program executes to the return statement, the expression will be evaluated and then return to the calling program to continue execution. The return value of the function is the value of the expression.

php custom function declaration example

The following is a simple example to introduce a custom function sun() to calculate the sum of the two parameters passed in , and then output all expressions and results.

<?php
  function sun($a,$b)
  {
     $num = $a + $b;
     return $num;
  }
  echo sun(5,8);
?>

The result is: 5+8=13

The above is how to declare a php custom function. The next chapter will tell friends How to callphp custom function.

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