problem with if else condition for variable from database

Question

I am retreiving a feild from a database, into $subcat. If $subcat is null, I want to show the form to add to a category, otherwise I want to display the category. $subcat definitly exists and is correctly retrieved. It is either null or a string.

if ($subcat != null) {
$showCategory = "<p><strong>Auction Category: </strong> ".$tmp['subcat'];
}
else 
{
$showCategory = "<form name=\"categoryForm\">
  <input name=\"radiobutton\" type=\"radio\" value=\"fakeapproved\" />Fake (Approved)<p>
  <input name=\"radiobutton\" type=\"radio\" value=\"fakesuspected\" />Fake (Suspected)<p>
  <input name=\"radiobutton\" type=\"radio\" value=\"keyword\" />Forbidden Keywords<p>
  <input name=\"radiobutton\" type=\"radio\" value=\"parallelimport\" />Parallel Imports
  <input name=\"Submit\" type=\"submit\" value=\"Update\" onclick=\"handleClick(".$pk.");return false\"/>
</form>";
}

However, all that is shown is the form. When $subcat is definitly, without a doubt not null, the form is still shown. I tried swapping the else clauses around, but then the category was displayed, even when $subcat was verifiably null.

Answer 1

In php you can check for a variable being null using is_null

So use:

if (!is_null($subcat)) {

Answer 2

is null works if the variable is actually NULL. If the variable is the empty string (""), zero, false, or an empty array, is_null evaluates to false. This is somewhat counter-intuitive, so I would always suggest using empty() instead.

empty() returns true for 0, empty string, empty array, boolean false, or NULL. So try:

if(!empty($subcat)){ do something; }

Only use is_null if you are 100% sure you ONLY want to do something if the variable is NULL. Empty is generally better to check whether you're about to call a class method on something unexpected.

Edit: Oh also, sometimes retrieving NULL from a database gives you the string "NULL" which is not the same as an actual NULL value. It depends on the db you're using and how you saved the value to the database in the first place. This is very easy to miss and can take forever to figure out. Try var_dump()'ing your subcat variable to see if it is "NULL" string (4) or literally a NULL value. This could account for unexpected behavior in your other code segment you mentioned in the comments.