Introduction to the difference between global and $GLOBALS in php

1.global

The function of Global is to define global variables, but this global variable does not apply to the entire website, but to the current page, including all files in include or require.

However, global variables defined within the function body can be used within the function body, while global variables defined outside the function body cannot be used within the function body. See the example below for details.

(1) Define global variables within the function body, which can be used within the function body.

<?PHP 
$a=123; 
function aa() 
{ 
Global $a; //把$a定义为global变量。 echo $a; //调用函数体外的变量} 
aa(); //输出结果为123，说明函数体内可以使用函数体外的变量；?>

(2) Define global variables outside the function body and cannot use them inside the function body.

<?PHP 
$a=123; 
Global $a; //在函数体外把$a定义为global变量。 function aa() 
{  
　　echo $a; 
} 
aa();//会报错，不能输出变量a。?>

2.$GLOBALS

In the $GLOBALS array, each variable is an element, the key name corresponds to the variable name, and the value corresponds to the variable's content . $GLOBALS exists in the global scope because $GLOBALS is a superglobal variable. Pay attention to the writing method of $GLOBALS. For example, the variable $a1 is written as $GLOBALS['a1'].

Example: First use global definition

<?PHP 
$a1 = 1; 
$a2 = 2; 
function Sum() 
{ 
　　global a1, a2;a2 = a1 + a2; //定义变a1和a2；}
Sum(); 
echo a2; //输出结果为3?>

Use $GLOBALS to define global variables

<?PHP 
$a1 = 1; 
$a2 = 2;function Sum() 
{ 
　　$GLOBALS['a1'] = $GLOBALS['a1'] + $GLOBALS['a2']; //定义变量时每个都要定义}
Sum(); 
echo a2; //输出结果为2?>

eg: global

function test() 
{ 
    global $a;//定义全局变量a 
    unset($a); //删除变量a
    //print $a;//会报错，因为unset已经把$a删除了。 } 
$a = 2; //定义一个变量atest(); //调用test()方法print $a; //输出a，输出的其实是$a = 2,所以结果为2.

eg: $GLOBALS

function test_global() 
{ 
    global $var1, $var2; 
    $var2 =& $var1; 
} 
function test_globals() 
{ 
    $GLOBALS['var3'] =& $GLOBALS['var1']; 
} 
$var1 = 5; 
$var2 = $var3 = 0; 

test_global(); 
print $var2; //输出结果为0test_globals(); 
print $var3; //输结果为5

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