The scope of global variables in PHP_PHP tutorial-PHP Tutorial-php.cn

The scope of global variables in PHP_PHP tutorial

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Release： 2016-07-13 16:56:55

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Recently I was developing a Discuz! plug-in, and I encountered a problem today. When I called the variable data of the plug-in in a function in the background, it returned a null value. After testing it several times to no avail, I suddenly remembered that the cache should not be loaded. So loadcache('plugin') was added to load the plug-in cache. But the problem remains.

Analyzing the problem, the function that needs to call the data is a function (tentatively called function A). Global $_G; has been executed to call the global variable, and the output of $_G through print_r also confirms that there is data in $_G. Yes, what is missing is the plug-in cache. Function A also needs to be called in the front desk, because the front desk is covered with the shell of plugin.php and the plug-in cache has been loaded. There is no need to execute loadcache('plugin'). Therefore, executing the loadcache('plugin') operation in the function has an impact on execution efficiency. Influence.

Analyzing the problem again, the code for calling function A in the background is in another function (let’s call it function B for the time being). I suddenly wondered if I would execute global $_G; in this function so that the background can be loaded. Variable content is passed from function B to function A?

With the attitude of giving it a try, I also added global $_G; in function B, and it worked!

This raises the issue of the scope of global scope. In my debugging this time, function A is called by function B, so the new $_G generated by loadcache('plugin'); called in the background is only valid in the background part, and because global $_G is not used in function B, Therefore, the latest $_G is not obtained. I wrote the file reference (require) of function A in function B. Function A becomes a subset of function B. The global variables of loadcache run in the background code are invalid for function A. The $ obtained by global in function A The _G value bypasses the loadcache I wrote. Therefore, you need to run global once in function B to obtain the latest $_G value before it can take effect in function A.

Here is a demonstration example using the "global" keyword:

The code is as follows	Copy code

代码如下	复制代码
$my_var = 'Hello World'; test_global(); function test_global() { // Now in local scope // the $my_var variable doesn't exist // Produces error: "Undefined variable: my_var" echo $my_var; // Now let's important the variable global $my_var; // Works: echo $my_var; } ?>

$my_var = 'Hello World';

test_global();

function test_global() {

// Now in local scope

// the $my_var variable doesn't exist

// Produces error: "Undefined variable: my_var"

echo $my_var;

// Now let's important the variable

global $my_var;

代码如下

复制代码

$a = 1;
$b = 2;

function Sum()
{
global $a, $b; //在里面声明为全局变量

$b = $a + $b;
}

Sum();
echo $b;
?>

// Works: echo $my_var; } ?> As you can see in the above example, the "global" keyword is used to import global variables. Looks like it works Great job and very simple, so why should we worry about using the "global" keyword to define global data Let me explain to those who are new to the industry the use of global variables, "global variables", the two globals in this term The word already tells us that this variable can be used everywhere. Let’s look at an example first:

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$a = 1;<🎜> $b = 2;<🎜> <🎜>function Sum()<🎜> {<🎜> Global $a, $b; //Declare it as a global variable inside<🎜> <🎜> $b = $a + $b;<🎜> }<🎜> <🎜>Sum();<🎜> echo $b;<🎜> ?>

Result: 3

If there is no global variable global, the values of $a and $b cannot be obtained within the method, so if you want to use external variables in the method, just

You need to declare this variable as a global variable first, so that it can be used, which is very convenient.

function Sum()
{
global $w3sky, $w3sky2;$w3sky2 = $w3sky + $w3sky2;
}Sum();
echo $w3sky2;
? ?>

The code is as follows

代码如下

复制代码

$w3sky = 1;
$w3sky2 = 2;

function Sum()
{
global $w3sky, $w3sky2;$w3sky2 = $w3sky + $w3sky2;
}Sum();
echo $w3sky2;
?>

Copy code

$w3sky = 1;
$w3sky2 = 2;

true

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TechArticleI am developing a Discuz! plug-in recently. I encountered a problem today. I called the plug-in in a function in the background. A null value is returned when the variable data is used. After testing a few times with no results, I suddenly remembered that it should be...