Determine if the PHP variable is undefined or empty

Determine if the PHP variable is defined and is empty

Isset () "1"

Returns? TRUE? If? var? exists and have value other than? NULL,? FALSE? otherwise.

Input can be multiple variables, only when all variables are true, return true

Empty () "2"

Returns? FALSE? If? varhas a non-empty and Non-zero value.

The following things is considered to be empty:

• "" (An empty string)
• 0 (0 as an integer)
• "0" (0 as a string)
• Null
• FALSE
• Array () (an empty array)
• var $var; (a variable declared, but without a value in a class)

Input can only be a variable

Is_null () "3"

Returns? TRUE? If? var? is? NULL?,? FALSE? otherwise.

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?? A variable is considered to be? null? if:

• It has been assigned the constant? NULL.

• It has no been set to any value yet.

• It has been? unset (). ? ?

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$x Use PHP functions for variables?? to compare Expression GetType () empty () Is_null () isset () if ($x) Boolean

$x = "";	String	TRUE	FALSE	TRUE	FALSE
$x = null;	Null	TRUE	TRUE	FALSE	FALSE
var $x;	Null	TRUE	TRUE	FALSE	FALSE
$x? is undefined	Null	TRUE	TRUE	FALSE	FALSE
$x = Array ();	Array	TRUE	FALSE	TRUE	FALSE
$x = false;	Boolean	TRUE	FALSE	TRUE	FALSE
$x = true;	Boolean	FALSE	FALSE	TRUE	TRUE
$x = 1;	Integer	FALSE	FALSE	TRUE	TRUE
$x = 42;	Integer	FALSE	FALSE	TRUE	TRUE
$x = 0;	Integer	TRUE	FALSE	TRUE	FALSE
$x =-1;	Integer	FALSE	FALSE	TRUE	TRUE
$x = "1";	String	FALSE	FALSE	TRUE	TRUE
$x = "0";	String	TRUE	FALSE	TRUE	FALSE
$x = "1";	String	FALSE	FALSE	TRUE	TRUE
$x = "PHP";	String	FALSE	FALSE	TRUE	TRUE
$x = "true";	String	FALSE	FALSE	TRUE	TRUE
$x = "false";	String	FALSE	FALSE	TRUE	TRUE

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(The above table did not find the original source, who knows please tell me)

What if the variable is an object?

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Expression GetType () empty () Is_null () isset () if ($x) Boolean

$x = new Object ()?	Object	FALSE	FALSE	TRUE	TRUE

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Reference:

"1" http://php.net/manual/en/function.isset.php

"2" http://www.php.net/manual/en/function.empty.php

"3" http://www.php.net/manual/en/function.is-null.php

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Http://blog.csdn.net/autofei/archive/2010/05/24/5619004.aspx

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