Detailed explanation of PHP variable scope (1/3)_PHP tutorial-PHP Tutorial-php.cn

The scope of a variable is the context in which it is defined (that is, the scope in which it takes effect). 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';

代码如下

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$a = 1; /* global scope */

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

Test();
?>

Here 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:

The code is as follows

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$a = 1; /* global scope */

function Test()

{

代码如下

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$a = 1;
$b = 2;

function Sum()
{
global $a, $b;

$b = $a + $b;
}

Sum();
echo $b;
?>

echo $a ; /* reference to local scope variable */

}

Test();

This script There will be no output because the echo statement refers to a local version of the variable $a, and it is not assigned a value in 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.

代码如下

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$a = 1;
$b = 2;

function Sum()
{
$GLOBALS['b'] = $GLOBALS['a'] + $GLOBALS['b'];
}

Sum();
echo $b;
?>

global keyword

First, an example of using global:

Example #1 Using global

Related labels：

php 。 context Scope variable definition Take effect of background scope Detailed explanation

source：php.cn

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