If no arguments are provided in the function, how do I test to see if it is left blank?

Question

<?php    
/* Copyright Date
--------------------------*/
function copyright_date($creation_year) {
    $current_year = date('Y');

    if ($creation_year == $current_year || $creation_year == '') {
     echo $current_year;
    } 
    else {
     echo $creation_year . '-' . $current_year;
    }   
}
?>

If someone forgets to add the argument (the year the website was created), e.g.

<?php copyright_date(); ?>

instead of:

<?php copyright_date(2009); ?>

how would I test to see if the argument was left blank? In my if statement, that's what $creation_year == '' is for, but since the argument isn't a string, it doesn't work.

Answer 1

You could use the isset function

if ($creation_year == $current_year || !isset($creation_year)){
 //...
}

Answer 2

Make $creation_year an optional argument with a default value of NULL.

function copyright_date($creation_year=NULL) {

Now inside the function just test if $creation_year is equal to NULL, which will happen when the function is called with no arguments.