Global keyword and $globals usage in PHP

First, let's look at some code.

<?php$a  =  1;  /* Global scope */function  Test () {    echo  $a;  /* Reference to local scope variable */}test ();? >

This script does not have any output, because the Echo statement refers to a local version of the variable $a, and within that range, it is not assigned a value. You may notice that the global variables in PHP are a little different from the C language, and in C, global variables are automatically applied in functions unless overridden by local variables. This can cause some problems, and some people may accidentally change a global variable. Global variables in PHP must be declared globally when used in functions.

Global keyword

First, an example of using global is the following code:

<?php$a  =  1; $b  =  2; function  Sum () {    global  $a,  $b;     $b  =  $a  +  $b;} Sum (); Echo  $b;? >

The output of the above script will be "3". After you declare a global variable $a and $b in a function, all references to either variable point to its global version. PHP has no restrictions on the maximum number of global variables a function can declare.

The second way to access variables globally is to customize $GLOBALS arrays with special PHP. The previous example can be written as:

Example #2 use $GLOBALS instead of global, the code is as follows:

<?php$a  =  1; $b  =  2; function  Sum () {     $GLOBALS [' b '] =  $GLOBALS [' a '] +  $GLOBALS [ ' B '];} Sum (); Echo  $b;? >

$GLOBALS is an associative array, each variable is an element, the key name corresponds to the variable name, and the value corresponds to the contents of the variable. $GLOBALS exists globally because $GLOBALS is a hyper-global variable. The following example shows the usefulness of a hyper-global variable:

Example #3 Examples of hyper-global variables and scopes

<?phpfunction  Test_global () {     ///Most of the predefined variables are not "super", they need to use the ' global ' keyword to make them valid in the local area of the function.     Global  $HTTP _post_vars;    echo  $HTTP _post_vars [' name '];     Superglobals are valid in any scope, and they do not require a ' global ' statement. Superglobals was introduced in PHP 4.1.0.     echo  $_post [' name '];}? >