Use is_null rather than == null

Posted by مصطفى in English, PHP Sep 21st, 2009 | 2 responses

While playing with strings one should be VERY VERY VERY cautious when trying to check for a “null” value

PHP has the bad habit of considering empty strings to be “null” and “false” , for instance

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$foo = '';
if( $foo == null && $foo == false ){
    echo "So PHP actually considers empty strings to be null and false";
}


To avoid this either use

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is_null( $foo )
//or
$foo === null

Try this code

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$foo = '';
if( $foo == null && $foo == false){
    echo 'So PHP actually considers empty strings to be null AND false!';
}
 
if( !is_null( $foo )){
	echo 'Using is_null() will return true only if $foo is null';
}
 
if( $foo !== null ){
	echo 'Using === and !== also works well';
}


2 Responses to “Use is_null rather than == null”

  1. Ahmad Alfy says:
    September 21, 2009 at 1:40 pm

    so, $foo = ” doesn’t make $foo null!
    right?

  2. مصطفى says:
    September 21, 2009 at 2:53 pm

    Strictly speaking
    $foo = ” is an empty (String)
    $foo = null is nothing , not a number not a object , just nothing

    In most ,if not all, programming languages null is not equal to an empty string or integer who’s value is zero.

    PHP on the other appears to allow this

    consider this example

    function getPhoneNumberFromDatabase(){

    if( $db->getConnection() == false ){
    return null;
    }

    return $db->getPhoneNumber();
    }

    in many cases you will want your functions to return NULL upon failure

    so if we do this

    $phone = getPhoneNumberFromDatabase();
    if( $phone == null ){
    echo ‘Database connection failed’;
    }

    In this case , PHP will report that “Database connection failed” even if the connection is okay but the phone number was an empty string.

    That’s why you should use is_null or === null

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