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1. Functions
The function does not need to be defined before the call unless the function is conditionally defined in the following two examples.
When a function is conditionally defined, its definition must be processed before the call.
Example #2 Conditional Functions
<?php$makefoo = true;/* cannot invoke the Foo () function here because it does not yet exist, but can call the bar () function. */bar (); if ($makefoo) { function foo () { echo "I don ' t exist until program execution reaches me.\n"; }}
/* can now safely call function foo (),
Because the $makefoo value is true */
if ($makefoo) foo ();
function Bar ()
{
echo "I exist immediately upon program start.\n";
}
?>Functions in the Example #3 function
<?phpfunction foo () { function bar () { echo "I don ' t exist until Foo () is called.\n"; }} /* Cannot now call the bar () function because it does not yet exist */foo ();/* can now call the bar () function, because the execution of the Foo () function causes the bar () function to become a defined function */bar (); > All functions and classes in PHP have global scope, can be defined within a function and are called outside, and vice versa.
PHP does not support function overloading, and it is not possible to cancel the definition or redefine a declared function.
Note: the function name is case-insensitive, but it is a good practice to use the same form as it was defined when calling a function.
PHP's functions support a variable number of parameters and default parameters. See Func_num_args (),Func_get_arg (), and Func_get_args ().
Recursive functions can be called in PHP. However, to avoid recursive function/method calls over 100-200 layers, because the stack might crash and then terminate the current script.
2. Class
A class can inherit the methods and properties of another class in a declaration using the extends keyword. PHP does not support multiple inheritance, and a class can inherit only one base class.
2.1 Properties
A variable member of a class is called a "property", or "field", "characteristic", which is known collectively as "Properties" in this document. A property declaration is made up of the keyword public,protected , or private , followed by a common variable declaration. A variable in a property can be initialized, but the initialized value must be a constant, where a constant is a PHP script that can get its value at compile time without relying on the information at run time to evaluate it.
Class 2.2 Constants
You can define a value that is always the same in a class as a constant. You do not need to use symbols when defining and using constants $ .
The value of a constant must be a fixed value, not a variable, a class property, a result of a mathematical operation, or a function call.
You can also define constants in the interface (interface).
2.3 Constructors and destructors
If a constructor is defined in a subclass, the constructor of its parent class is not implicitly called. To execute the constructor of the parent class, you need to call parent::__construct ()in the constructor of the child class. If a subclass does not have a constructor defined, it inherits from the parent class like a normal class method (if it is not defined as private).
As with constructors, the destructor of the parent class is not called by the engine. To execute a destructor for a parent class, you must explicitly call parent::__destruct ()in the destructor body of the subclass. Also, as with constructors, subclasses inherit the parent class if they do not have a destructor defined by themselves.
2.4 Static statically keyword
Declaring a class property or method as static can be accessed directly without instantiating the class. Static properties cannot be accessed through an object that a class has instantiated (but static methods can).
To be compatible with PHP 4, if no access control is specified, the properties and methods default to public.
Because static methods do not need to be called through objects, pseudo-variables $this are not available in static methods.
A static property cannot be accessed by an object through the operator.
Invoking a non-static method in a static manner results E_STRICT in a level of error.
Just like all other PHP static variables, static properties can only be initialized to literals or constants, and expressions cannot be used. You can initialize a static property to an integer or an array, but you cannot initialize it to another variable or function return value, or point to an object.
<?phpclass foo{public static $my _static = ' Foo '; Public Function Staticvalue () { return self:: $my _static; }} Class Bar extends foo{public function foostatic () { return Parent:: $my _static; }} Print Foo:: $my _static. "\ n"; $foo = new Foo ();p rint $foo->staticvalue (). "\ n";p rint $foo->my_static. "\ n"; Undefined "Property" My_static print $foo:: $my _static. "\ n"; $classname = ' Foo ';p rint $classname:: $my _static. "\ n"; As of PHP 5.3.0print Bar:: $my _static. "\ n"; $bar = new bar ();p rint $bar->foostatic (). "\ n";? > </programlisting> </example> <example> <title> static Method Example </title > <programlisting role= "PHP" ><
