PHP: isset() function

isset() function

The isset () function is used to check whether a variable is set or not. If a variable is already unset with unset() function, it will no longer be set. The isset() function return false if testing variable contains a NULL value.


(PHP 4 and above)


isset(variable1, variable2......) 


Name Description Required /
variable1 The variable being checked Required Mixed*
Variable2 ...... More variable to be checked. Optional Mixed*

*Mixed: Mixed indicates that a parameter may accept multiple (but not necessarily all) types.

Return value:

TRUE if variable (variable1,variable2..) exists and has value not equal to NULL, FALSE otherwise.

Value Type: Boolean.

Pictorial presentation of PHP isset() function

Pictorial presentation of PHP isset() function


$var1 = 'test';

Output :


View the example in the browser

Practice here online :

See also

PHP Function Reference

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PHP: Tips of the Day

SQL injection that gets around mysql_real_escape_string()

Consider the following query:

$iId = mysql_real_escape_string("1 OR 1=1");    
$sSql = "SELECT * FROM table WHERE id = $iId";

mysql_real_escape_string() will not protect you against this. The fact that you use single quotes (' ') around your variables inside your query is what protects you against this. The following is also an option:

$iId = (int)"1 OR 1=1";
$sSql = "SELECT * FROM table WHERE id = $iId";

Ref : https://bit.ly/32q3bJ7