isset

Definition and usage

isset() function checks if the variable is set, which means that the variable must be declared and not NULL .

If the variable exists and is not NULL , the function returns true , otherwise false .

Note: If multiple variables are provided, this function returns true only if all variables are set.

Tip: You can use unset() function to unset variables.

Example

Check if the variable is empty. Also check if the variable is set/declared:

 <?php
$a = 0 ;
// True because $a is set
if ( isset ( $a ) ) {
  echo "Variable 'a' is set.<br>" ;
}

$b = null ;
// False because $b is NULL
if ( isset ( $b ) ) {
  echo "Variable 'b' is set." ;
}
?>

Try it yourself

grammar

 isset ( variable , ... . ) ;