isset vs. regular if statement for form validation

[gordonisgod]

Is there any advantage to use isset over if statements for form validation?

For example, what's the advantage of using:

if (isset($firstname)) {
} else {
print "Go back and type your first name.";
}
}

over

if (empty($firstname) {
print "Go back and type your first name.";
exit();
}

[stolzyboy]

actually i would say your advantage would be by using the empty() way, since isset isn't always accurate, where empty will tell you if it is empty or not, isset() will sometime evaluate as true even when the value of the variable is empty

[matt_4013]

However, both ways you have there aren't entirely accurate. If somebody enters a space into your text box, it's no longer empty. The isset function probably wouldn't work as you'd expect, because when the form is submitted, it's still posting the value of the textbox as a variable, and as such it should always be set.

My suggestion:

if(isset($_POST['submit'])) {

// We use trim to clear any spaces from the start and end of a string
if(empty(trim($_POST['username']))) {

	echo "Oh god, you silly fool! You forgot your username! What are we to do. . . PANIC!";
	die;
}

// Continue processing

} else {

// display your form
}

[stolzyboy]

yes you are very correct, i wasn't necessarily talking specifically about his code, i was speaking about the functions in general, the code was unorganized anyway and i wasn't about to tell him how to write his code, i understood he wanted to simply know the advantage of one over the other