What if a variable is null?

[New Oddity]

I have my site and the main page is a series of includes... The main content of the page is a include with the filename being a variable pulled from the URL (ie page.php?content=news.php) My problem comes when the client first visits and there is no content variable in the url. How do I check to see if there is a variable there or not so that I can set it.

[Anarchos]

if (!$content) { $content = "news.php"; }

[New Oddity]

Hrm... That easy? Groovy... Thanx.

[freakysid]

There are slight differences between testing a variable for its boolean value and checking whether it has been set. There might be circumstances where checking a variables boolean value is not going to give you the correct answer.

For example:

$milkInYourCoffee = false;

if ( ! $milkinYourCoffee ) {
    // The conditions will be satisfied and the if condition will be entered.
   // However it erroneous to conclude that $milkInYourCoffee has not been set
   // however it evaluates to false because that is the value it currently holds
}

$lumpsOfSugar = 0;

if (! $lumpsOfSugar ) {
   // again it would be erroneous to conclude that $lumpsOfSugar has not been set
   // and again it evaluates to false because 0 evaluates to false
} 

Quite often when we are validating data - especially when it is user data then testing whether a variable is holding a 0, '' (empty string) or NULL value "(which all evaluate to false) is an appropriate test. Technically, however, it is not the same as using isset()

From the above code had I called isset() I would have got a different result

$milkInYourCoffee = false;
$result = isset($milkInYourCoffee); // $result will be assigned TRUE

$lumpsOfSugar = 0;
$result = isset($lumpsOfSugar); // $result will be assigned TRUE 

To complicate things a little further, one thing that isset() will return false on is if a variable has been set but assigned a value of NULL. If you need to test whether a variable exists but its value is currently NULL then you need to use is_null()

Clear as mud?

[New Oddity]

Ah... That is what I was looking for. I thought I remembered goiung over that in the Man but could not remember the command. The problem I was running into was that when I tried to do anything with a variable that had no value, the program would create an error and exit the script. I know this is because I have error reporting at a high level, but I'm still building the site... Thanx y'all.