PHP variable types and scope of the detailed

  What is the scope of a variable? The scope of a variable refers to the valid range of variables within a lifetime of a script. Generally, there are global and local points

The scope of variables in PHP can be divided into: Super Global (the special type of global variables, in the local scope can be directly used), global, Local, static (is a special type of local variables) in PHP, the global variable is actually a static global variable, if not unset explicit release, So the script runs and ends global variables are released. Local static variable subdivision can be a local static function variable (a static variable declared in a function), a local static member variable (a static property declared in a class that is shared by all class instances) a local static variable that is automatically freed only when the script is run over   Super Global variables: In any scope of a script can be accessed, these are PHP built-in     code as follows: $GLOBALS $_server $_get $_post $_files $_session (persistent storage) $_ COOKIE (persistent storage) $_request $_env global variable: The declared variable is not inside a language structure such as class,function,if, if it is to be used inside languages such as class,function,if, Need to use keyword Global or Super global variable $globals   Static variables: variables declared with a keyword static in a function, the value of a static variable remains until the script ends a local variable: in class,function,if/while/ For such structure statements internal declarations of variables   1.global keywords and $globals instance code are as follows: <?php $a = 0; function foo () {    global $a;     echo $a;} function Foo2 () {    echo $GLOBALS [' a ']; 2 . static variables and ordinary local variables distinguish the instance code as follows: <?php function foo1 () {    $var = 0;     $var + +     return $ var Echo Foo1 (); Echo Foo1 (); Output is 1 function foo () {    static $var = 0;     $var + +;     return var;Foo (); echo foo (); First Output 1 second time 2 3.static keywords can also declare static properties and static methods static properties are only called by the class, but not by the class instance call static methods can not use $this, you can only access the static properties of the class with self   Another part of the code that understands the static variable:     code is as follows: <?php class T {        $v = = =         Public Function A ()         {                static $v AR = 10;                 $var + +;                 echo $var. "<br>n";        }         public static function AA ()         {                self:: $v + +;                 echo self:: $v. "<br>n";        }} $o 1 = new T (); $o 1->a ()//output $o 2 = new T (); $o 2->a ()//Output T::AA ()//Output one $o 1->AA ()//Output $o 2->AA ();//output   from the above code, we know that if there are static variables in a class member method, Even for different class instances, they share this static variable, although this static variable is not a class static member variable, this is easy to confuse.