The static keyword in PHP affects variables and functions

　
1 the global variable (external variable) before the description and then the static to form a global variable. The global variable itself is the static storage mode, static global variables are of course also static storage mode. The two are not different in the way they are stored. The difference between the two is that the scope of the Non-static global variable is the entire source program, and when a source program consists of multiple source files, non-static Global variables are valid in each source file. A static global variable restricts its scope, that is, it is only valid within the source file that defines the variable, and it cannot be used in other source files of the same source program. Because the scope of a static global variable is limited to one source file, it can only be common to functions within that source file, so it is possible to avoid causing errors in other source files.

2 from the above analysis can be seen, the local variable to the static variable is changed its storage mode that changes its lifetime. Changing the global variable to a static variable changes its scope and limits its use.

3 The static function differs from the normal function scope, only in this file. Functions that are used only in the current source file should be described as internal functions (static), and internal functions should be described and defined in the current source file. For functions that can be used outside the current source file, you should indicate in a header file that the source file to use these functions contains this header file

After PHP5.3.0, we can use a variable to invoke the class dynamically. However, the value of the variable cannot be the keyword self, parent, or static.

Example #1 static Member code example

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<?php Class 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. " "; $foo = new Foo (); Print $foo->staticvalue (). " "; Print $foo->my_static.      " "; Undefined "Property" My_static Print $foo:: $my _static. " "; $classname = ' Foo '; Print $classname:: $my _static. " "; PHP 5.3.0 can be invoked dynamically after Print Bar:: $my _static. " "; $bar = new Bar (); Print $bar->foostatic (). " "; ?> Example #2 static Method code example <?php Class Foo { public static function Astaticmethod () { // ... } } Foo::astaticmethod (); $classname = ' Foo '; $classname:: Astaticmethod (); As of PHP 5.3.0 ?>

For the use of the static keyword in a class, the PHP manual provides the following conventions:

1. Declaring a class member or method static, you can access it directly without instantiating the class. Static members (except static methods) cannot be accessed through an object.

2, because the static method does not need to pass the object to call, therefore the pseudo variable $this in the static method is not available.
3, static properties can not be accessed by the object through the-> operator.
4, with:: The way to call a non-static method can cause a e_strict level error.
Now let's look at the 4th agreement.
Operating environment: (WIN32) php/5.3.3

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Class foo{ public static $my _static = ' foo ';//declaring a static member Public Function Staticvalue () {//static method Return self:: $my _static;// } Public Function Run () {//Non-static method Return "ABC <br>"; } Public Function Callrun () { return Self::run ()///Use Self:: method to invoke a Non-static method } } echo Foo:: $my _static. "<br >"; echo Foo::run ()///non-static method called by ClassName:: Method Name Echo Foo::callrun ();

The static keyword of the interview question

Title Code: Write out the result of the operation of the following code ()

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<?php function Dewen () { $k =add_number (100); $k +=add_number (100); printf ("%d", $k); return 0; } function Add_number ($n) { static $i = 100; $i + + $n; return $i; }

The first thought is simply to add the calculation: The result is 400, the answer is wrong. Finally looked at the next, knocking on one side of the code, run to know is 500. Two $i+= $n were printed, $i before the calculation, once 100, once 200, knowing that the problem was static ghost. Then baidu a static keyword, before it dawned.

Static keyword action:

Static variables in PHP are more widely used, not only can we add the static modifier to the class, method, or variable, we can even add the static keyword to the function's internal variables. A variable with the static modifier added even if the function completes the value is not lost, that is, the variable still remembers the original value the next time the function is called. For example,

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<?php function test () 03 { static $var 1 = 1; $var 1 +=2; 1 echo $var. ' ' ; 07} 08 Test (); Test (); one Test (); ?> The results of the operation are as follows: 3 5 7

Sum up:

What is the difference between a static global variable and a normal global variable:
Static global variable is only first made once, preventing it from being referenced in other file cells;
What is the difference between a static local variable and a normal local variable:
A static local variable is initialized only once, the next time based on the last result value, and the
static function differs from a normal function:
The static function is only one copy in memory, The normal function maintains a copy of each invocation