How to test for value when blank?

[conjurer]

I am trying to pass some search criteria via a form.

I wanted to test each of the possible fields to see if they are set and then create a query around the info passed in from the form. I thought I could use is_null to test and find out is blank, but what I am getting is that is_null fails and isset returns true on a text field that is left blank.

How would it be best to test this?

Here is what I have now:

$city=$_POST['city'];
$set = isset($_POST['city']);
$null = is_null($_POST['city']);
  echo "<h3>City=$city;  isset = $set; and is_null = $null </h3>";

And where the city is left blank it returns:

City=; isset = 1; and is_null =

[NogDog]

I usually test for an empty string (and trim() it first in case all that's been entered is spaces):

$city = (isset($_POST['city'])) ? trim($_POST['city']) : '';
if($city !== '')
{
   // $city has a non-blank value, so do whatever you want with it
}
else
{
   // either $_POST['city'] was not in the $_POST array or it was empty
}

[bradgrafelman]

if(empty($_POST['city'])) {

// city is either: an empty string, 0, or not set

}