php custom function_PHP tutorial

User-defined functions are also called custom functions. They are not provided by PHP but are created by programmers. Since you create such functions yourself, you can fully control these functions. Therefore, you can make a function exactly the way you want. Run.

1. Declare function

In PHP, the method of defining functions is almost the same as in other programming languages. The following is the syntax structure of PHP function declaration:

Function function_name($argument1,$argument2,$argument3,...$argumentn)

{

//Function code code

Return return value;

}

In the above grammatical structure, the meaning of the keywords is as follows.

(1)function: keyword used to declare user-defined functions.

(2) function_name: The name of the function to be created. This name will be used when it is called later. The function name should be unique because PHP does not support overloading. When naming functions, you need to follow the same principles as variable naming. But functions The name cannot start with $, but the variable can.

(3)argument: The value to be passed to the function. The function can have multiple parameters, with commas between them. But the parameter items are optional, and you can not pass any parameters when calling the function.

(4) code: is a piece of code that is executed when the function is called. If there are two or more statements, the code must be enclosed in curly brackets "{}". However, if there is only one code, no curly braces are needed. Brackets.

(5)Return: Return the value required by the calling code. Any type can be returned, including lists and objects. This causes the function to immediately end its execution and pass control back to the line where it was called.

2. Parameterless function

Code func_1.php

require 'a.php';
echo "I will not be executed!";

?>

3. Function with parameters

PHP supports passing parameters by value (default), passing by reference and default parameter values. Variable length parameter lists are only supported in PHP4 and later versions.

(1) Pass parameters by value. Passing parameters by value is the default transfer method of PHP. Using this method, a value (parameter) must be passed when the main program is called.

Codesum.php

function sum ($a,$b)
{
Echo $a+$b;
}
sum(100,20); //Start calling this function
?>

(2) Reference parameters. When passing by value, only a copy of the parameters is passed to the called function. However, any modification to these values ​​within the called function will not affect the original values ​​in the calling function. Passing by reference In fact, it is address passing, passing the address of a variable as a parameter.

Code valuechange.php

$myNum=100;
function Valuechange ($number)
{
$number=$number+1;
Echo $number . "
";
}
Valuechange($myNum);
Echo $myNum;
?>

(3) Default value parameter. Using the default parameter value passing method, the function must have a parameter when called. If there is no value used, the default value is passed to the function parameter. The default value must be a constant expression, not a variable , class member or function call.

Tip: When using default parameters, any default parameters must be placed to the right of the non-default parameters; otherwise, the function may not work as expected.

Code func_default.php

$myNum=100;
function Valuechange ($number)
{
$number=$number+1;
Echo $number . "
";
}
Valuechange($myNum);
Echo $myNum;
?>

http://www.bkjia.com/PHPjc/478606.htmlwww.bkjia.comtruehttp: //www.bkjia.com/PHPjc/478606.htmlTechArticleUser-defined functions are also called custom functions. They are not provided by PHP and are created by programmers. Because You create such functions yourself, so you have complete control over these functions. Therefore you can...