Detailed explanation of global variables in PHP_PHP tutorial-PHP Tutorial-php.cn

This article will introduce in detail the method of global variable global in PHP. Friends who need to know how to use the global function can refer to this article.

The scope of a variable is the context in which it is defined (that is, its effective scope). Most PHP variables have only a single scope. This single scope span also includes files introduced by include and require. For example:

The code is as follows

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代码如下	复制代码
$a = 1; include 'b.inc'; ?>

$a = 1;
include 'b.inc';
?>

This variable $a will take effect in the included file b.inc. However, in user-defined functions, a local function scope will be introduced. Any variables used inside a function will be restricted to the local function scope by default. For example:

代码如下

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$a = 1; /* global scope */

function Test()
{
echo $a; /* reference to local scope variable */
}

Test();
?>

The code is as follows

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$a = 1; /* global scope */

function Test()
{
echo $a; /* reference to local scope variable */
}

Test();
?>

代码如下	复制代码
$a = 0 ; function Test() { $a =1; } Test(); echo $a; ?>

This script will produce no output because the echo statement refers to a local version of the variable $a, and it is not assigned a value within this scope. You may notice that PHP's global variables are a little different from C language. In C language, global variables automatically take effect in functions unless overridden by local variables. This may cause some problems, someone may accidentally change a global variable. Global variables in PHP must be declared global when used in functions.

Today I encountered the problem that php global variables do not work.

代码如下	复制代码
$a = 0 ; function Test() { global $a;//申明函数体Test内使用的$a变量为global全局变量 $a =1; } Test(); echo $a; ?>

First a simple piece of code: The output in the above code is 0, that is because the $a variable in the function body Test is set to a local variable by default, and the scope of $a is within Test. Modify the code as follows

After declaring the $a variable used in the function body Test as a global global variable, $a has a global effect, so the output is 1.
The above examples are just basic knowledge of global variables. Let’s look at more complicated ones:

//A.php file

The code is as follows

代码如下

复制代码

function Test_Global()
{
include 'B.php';
Test();
}

$a = 0 ;
Test_Global();
echo $a;
?>

//B.php 文件

function Test()
{
global $a;//申明函数体Sum内使用的$a变量为global全局变量
$a =1;
}
?>

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function Test_Global()

{

Include 'B.php';

Test();

}

代码如下

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//A.php 文件

function Test_Global()
{
Test();
}
include 'B.php'; //将include 从局部Test_Global函数中移出
$a = 0 ;
Test_Global();
echo $a;
?>

//B.php 文件

function Test()
{
global $a;
$a =1;
}
?>

$a = 0 ;

Test_Global();

echo $a;

代码如下

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//A.php 文件
include 'B.php';
$a =0;
Set_Global($a);
echo $a;
?>

//B.php 文件

function Set_Global(&$var)
{
$var=1;
}
?>

?> //B.php file function Test()

Related labels：

global php introduce overall situation about variable article of Detailed explanation

source：php.cn

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