Check for NULL or empty '' in function? [duplicate]

Question

I'm running the following function and want to check if a value is NULL or '', but it seems to react the same for both. This prints C1C2. How can I get it to print B1C1C2? Should I use isset() somehow?

function title($a = NULL, $b = NULL, $c = NULL) {
    if( $a != NULL )
    {
        echo 'A1';
        if( $a != '' )
        {
            echo 'A2';
        }
    }
    if( $b != NULL )
    {
        echo 'B1';
        if( $b != '' )
        {
            echo 'B2';
        }
    }
    if( $c != NULL )
    {
        echo 'C1';
        if( $c != '' )
        {
            echo 'C2';
        }
    }
}

title(NULL, '', 'C');

Just use !isnull($a) or !empty($a)

GrumpyCrouton
– GrumpyCrouton

2018-06-13 18:26:39 +00:00
Commented Jun 13, 2018 at 18:26 — GrumpyCrouton
– GrumpyCrouton, Commented Jun 13, 2018 at 18:26
@GrumpyCrouton maybe you meant is_null()

Julian David
– Julian David

2018-06-13 18:31:16 +00:00
Commented Jun 13, 2018 at 18:31 — Julian David
– Julian David, Commented Jun 13, 2018 at 18:31
@JulianDavid That I did, thank you :)

GrumpyCrouton
– GrumpyCrouton

2018-06-13 18:33:03 +00:00
Commented Jun 13, 2018 at 18:33 — GrumpyCrouton
– GrumpyCrouton, Commented Jun 13, 2018 at 18:33

sam · Accepted Answer · 2018-06-13 18:20:53Z

3

If you just check for the value of the variable you will get true whether null or an empty string (''):

null == ''; // 1 (true)

You also need to check for type:

null === ''; // (false)

So instead of:

if( $a != NULL )

Run:

if( $a !== NULL )

Which will also check for type; '' is a string - not null type.

Rearranged function:

function title($a = NULL, $b = NULL, $c = NULL) {
    if( $a !== NULL )
    {
        echo 'A1';
        if( $a !== '' )
        {
            echo 'A2';
        }
    }
    if( $b !== NULL )
    {
        echo 'B1';
        if( $b !== '' )
        {
            echo 'B2';
        }
    }
    if( $c !== NULL )
    {
        echo 'C1';
        if( $c !== '' )
        {
            echo 'C2';
        }
    }
}

title(NULL, '', 'C'); // outputs: B1C1C2

answered Jun 13, 2018 at 18:20

sam

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Comments

marc_s · Accepted Answer · 2018-06-14 05:05:20Z

Be careful because ...

if(null == 0) echo "yes"; else echo "nope"; //prints yes
if(null === 0) echo "yes"; else echo "nope"; //prints no

So always use triple equals (=== or !==) instead of double equals (== or !=) in order to avoid this issue.

But the most appropriate way would be to use the "is_null()" PHP builtin function which returns true or false.

if(is_null(0)) echo "yes"; else echo "nope"; //prints nope

So we have ...

function title($a = NULL, $b = NULL, $c = NULL) {
    if(!is_null($a)) // using is_null builtin function
        echo 'A1';
        if($a !== '')// not !=, because 0!='' is false
            echo 'A2';
    if(!is_null($b))
        echo 'B1';
        if($b !== '')
            echo 'B2';
    if(!is_null($c))
        echo 'C1';
        if($c !== '')
            echo 'C2';
}

title(NULL, '', 'C'); // prints B1C1C2

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