PHP - check if variable is undefined

You can use -

$isTouch = isset($variable);

It will return true if the $variable is defined. if the variable is not defined it will return false.

Note : Returns TRUE if var exists and has value other than NULL, FALSE otherwise.

If you want to check for false, 0 etc You can then use empty() -

$isTouch = empty($variable);

empty() works for -

• "" (an empty string)
• 0 (0 as an integer)
• 0.0 (0 as a float)
• "0" (0 as a string)
• NULL
• FALSE
• array() (an empty array)
• $var; (a variable declared, but without a value)

An another way is simply :

if($test){
    echo "Yes 1";
}
if(!is_null($test)){
    echo "Yes 2";
}

$test = "hello";

if($test){
    echo "Yes 3";
}

Will return :

"Yes 3"

The best way is to use isset(), otherwise you can have an error like "undefined $test".

You can do it like this :

if( isset($test) && ($test!==null) )

You'll not have any error because the first condition isn't accepted.

To check is variable is set you need to use isset function.

$lorem = 'potato';

if(isset($lorem)){
    echo 'isset true' . '<br />';
}else{
    echo 'isset false' . '<br />';
}

if(isset($ipsum)){
    echo 'isset true' . '<br />';
}else{
    echo 'isset false' . '<br />';
}

this code will print:

isset true
isset false

read more in https://php.net/manual/en/function.isset.php