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Home  >  Article  >  Backend Development  >  Detailed explanation of PHP variable scope (1/3)_PHP tutorial

Detailed explanation of PHP variable scope (1/3)_PHP tutorial

WBOY
WBOYOriginal
2016-07-20 11:11:02890browse

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 Copy code
 代码如下 复制代码

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

?>
 代码如下 复制代码

$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 Copy code

$a = 1; /* global scope */


function Test()

{
代码如下 复制代码

$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 复制代码

$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

The code is as follows Copy code
The above script The output will be "3". Global variables $a and $b are declared in the function, and all reference variables of any variable will point to the global variables. PHP has no limit on the maximum number of global variables that a function can declare.
The second way to access variables in the global scope is to use a special PHP custom $GLOBALS array. The previous example can be written as: Example #2 Use $GLOBALS instead of global
The code is as follows Copy code
$a = 1;<🎜>$b = 2;<🎜><🎜>function Sum()<🎜>{<🎜> $GLOBALS['b'] = $GLOBALS['a'] + $GLOBALS['b'];<🎜>}<🎜 ><🎜>Sum();<🎜>echo $b;<🎜>?>
1 2 3 http://www.bkjia.com/PHPjc/444672.htmlwww.bkjia.comtruehttp: //www.bkjia.com/PHPjc/444672.htmlTechArticleThe 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 range span also contains incl...
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