Php (4) -- function

: This article mainly introduces php (4)-functions. For more information about PHP tutorials, see. Functions in PHP do not need to be defined before being called;

All functions and classes in PHP have a global scope, which can be defined within a function and called outside, and vice versa;

PHP does not support function overloading, and it is impossible to cancel or redefine declared functions;

You can call recursive functions in PHP. However, to avoid calling recursive functions/methods that exceed 100-200 layers, the current script may be terminated because the stack may crash.

Function definition:

Function name ([parameter list]) {

Function body

}

PHP uses the value transfer method by default, but can also pass references (this method can change the passed parameter value in the function body)

For example:

Function fun (& $ var ){

$ Var ++;

}

$ Var = 0;

Fun ($ var );

Echo $ var;

Output 1;

PHP supports default parameter values.

For example:

Function fun ($ var1, $ var2 = 2, $ var3 = 3 ){
Return $ var1 + $ var2 + $ var3;
}

Echo fun (1 );
Echo fun (1, 1 );
Echo fun (1, 1, 2 );

Output 6 5 4

Note: Any default parameter must be placed on the right of any non-default parameter; otherwise, the function will not work as expected.

For example, change the preceding function:

Function fun ($ var2 = 2, $ var3 = 3, $ var1 ){
Return $ var1 + $ var2 + $ var3;
}
Echo fun (1 );
Echo fun (1, 1 );
Echo fun (1, 1, 2 );

In addition to the normal execution of the third call method, problems may occur in the first two methods.

PHP supports a variable number of parameter lists.

Before PHP5.6, you need to use func_num_args () to obtain the parameter information and func_get_arg (I) to obtain the value of the I parameter;

For example:

Function fun (){
$ Len = func_num_args ();
$ Res = 0;
For ($ I = 0; $ I <$ len; $ I ++ ){
$ Res + = func_get_arg ($ I );
}
Return $ res;
}

The... $ args method is introduced in PHP5.6,

For example:

Function fun (... $ args ){
$ Res = 0;
Foreach ($ args as $ val ){
$ Res + = $ val;
}
Return $ res;

}

The results of the two methods are the same.

The concept of variable functions in PHP

That is, if a variable name has parentheses, PHP searches for a function with the same name as the variable value and tries to execute it. Variable functions can be used for some purposes, including callback functions and function tables.

Example:

Function fun (){
Echo "Hello ";
}
$ Var = "fun ";
$ Var (); // The fun () function will be called.

Anonymous functions in PHP

An Anonymous function (Anonymous functions) is also called a closure function (Closures), Allows you to temporarily create a function without a specified name. The value that is most often used as the callback function parameter.

You can also assign values to an anonymous function, such:

$ Fun = function (){
Echo "HelloWorld ";
};
$ Fun ();

The above introduces php (4)-functions, including some content, and hope to be helpful to friends who are interested in PHP tutorials.