PHP notes: Functions used in PHP

The Declaration of a function
1. Grammatical structure

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function functions name (argument list) { function body; Optional return value; Return optional }

parameter list separated by commas, do not omit the $ variable symbol
Function names are case-insensitive, rules are consistent with variables
function call to execute, you can first invoke the post declaration
Function name cannot be duplicate, including system function

2. Function call

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function sum ($x, $y)//formal parameter: arguments declared when declaring a function { $x = 1; If you assign a value to a parameter within a function, the argument is overwritten. $y = 2; $sum = 0; $sum = $x + $y; return $sum; Execution to return function end, no longer executed after } SUM (); SUM (2,2); Arguments: Values passed to the formal parameter when the function is called echo sum (2,2); Returning data by return can be used as a value

Ii. variables in the function
1. Variable Range

Local variables: variables declared and used within a function
Global variables: Declared outside the function, the script can be used anywhere

Tips: Use global variables in PHP functions to include this global variable in a function through the Global keyword in order to use

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$a = 1; $b = 2; function demo ($a = ') { Global must be placed in front Global $a, $b Global can contain multiple globally variable $GLOBALS [' a ']//declaring global variable method two Global $a; $a + 5; echo $a; } Demo ();

2. PHP static variable

Static variables can be invoked multiple times in the same function
A static variable can only be declared in a function or class and cannot be declared globally.

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function demo ($a = ') { static $a = 0; Defining static variables $a + +; echo "$a <br>"; } Demo (); Output 1 Demo (); Output 2

3. Variable function

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$var = ' Hello '; After the variable name, look for a function with the same name as the variable value $var (); Equivalent to Hello ();

Classification and declaration of functions

1. Function classification

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General functions BOOL Copy (string source,string dest) With mixed, indicating that any type of data can be transmitted BOOL Chown (string filename,mixed user) function with & parameter, this parameter can only be a variable, the value of the variable is dynamic Array sorting, index retention of arrays, and cell associations BOOL Arsort (array & $array [, int $sort _flags]) $fruits = Array (' A ', ' C ', ' B '); Arsort ($fruits); Var_dump ($fruits); The default function, which is a function with a bracket in it, that indicates that the parameter is optional, and that the default value is used if no value is passed If the call is not assigned, and there is no initial value, a warning appears Function demo ($a =1, $b =2) { #code } Demo (); With... parameter that represents any number of arguments that can be passed Inserts one or more cells at the beginning of an array int Array_unshift (array & $array, mixed $var [, mixed $ ...])

2. Declaring multiple parameter functions

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function Test () { Echo Func_num_args (); } Test (' A ', ' B ', ' C '); 3 Func_get_arg (): Returns the nth argument in the argument list function Test () { Echo func_get_arg (' 1 '); } Test (' A ', ' B ', ' C '); B

Working with instances

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function Cls_mysql () { $mysql = Func_get_args (); $conn = mysql_connect ($mysql [' 0 '], $mysql [' 1 '], $mysql [' 2 ']); } Cls_mysql (' localhost:3306 ', ' root ', ' 123456 ');

3, Function Annotation specification

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/** * Use the Demo function/function function to decide whether to use * * @static * @access Public * @param string $attributeName property name//function argument, deciding how to call the * @return The return value of string//function, decide what to do after the call */ Public Function Demo ($attributeName) { $attributeName = ' abc '; Return $attributeName }

Four, Callback callback function

We customize a function A, but instead of going directly to the function A, we call function A in function B, and function B implements a call to function A by receiving the name and parameters of function A, which is called a callback function.

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function A ($x, $y) { return $x * $y; } function B ($a, $b, $fun) { Return $a + $b + $fun ($a, $b); } Echo B (2,3, "A");

Implementation method of PHP callback function

PHP provides two built-in functions Call_user_func () and Call_user_func_array () provide support for callback functions

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Mixed Call_user_func_array receives the parameters of the callback function as an array Mixed Call_user_func_array (callable $callback, array $param _arr) Call_user_func_array (' F1 ', Array (' A ', ' B ')); The number of call_user_func parameters is determined according to the parameters of the callback function Mixed Call_user_func (callable $callback [, Mixed $parameter [, mixed $ ...]] Call_user_func_array (' F1 ', ' A ', ' B ');

Instance:

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Common global functions Function F1 ($arg 1, $arg 2) { echo $arg 1. " <br> ". $arg 2." <br> "; } echo "Calls function f1:<br> via Call_user_func_array"; Call_user_func_array (' F1 ', Array (' A ', ' B ')); echo "Calls function f1:<br> via Call_user_func"; Call_user_func (' F1 ', ' C ', ' D '); Class Class MyClass { Public $name; Function Show ($arg 1) { Echo ' parameter name: '. $arg 1. ' <br> "; Member name in echo ' object: '. $this->name; echo "<br>"; } function Show1 ($arg 1, $arg 2) { echo $arg 1. " <br> ". $arg 2." <br> "; } public static function Show2 ($arg 1, $arg 2) { echo $arg 1. " <br> ". $arg 2." <br> "; } } Echo invokes the Non-static member function in the class, which has this called the member:<br> in the object. $a = new MyClass; $a->name = ' F '; Call_user_func_array (Array ($a, ' show '), Array (' E ')); Echo invokes the Non-static member function of the class, which has no members in the calling object, no this:<br>. Call_user_func_array (Array (' MyClass ', ' Show1 '), Array (' G ', ' H ')); echo "Calls static member function:<br> in a class"; Call_user_func_array (Array (' MyClass ', ' show2 '), Array (' I ', ' J '));

Five, internal functions

The function is declared inside the function to be called inside the function to help the external function to complete some child functions