Entry

How can I check if a variable is defined?

Does isset() return true for empty variables?

What is the difference between isset() and empty()?

Jul 10th, 2003 11:09
Philip Olson, Nathan Wallace,

Example:
if (isset($var)) {
    echo "the var is set, and equals $var.  It may be empty though.";
}
    http://www.php.net/isset
isset() will tell you is a varaible has been defined. This can bite some
users, because it will return true even if the varable has an empty
value. Look at empty() as well. Sometimes you'll want to use one rather
than the other.  Note that even "0" and 0 are considered empty.
    http://www.php.net/empty
For example, say I have an HTML form that passes various form 
elements.  Even when a user leaves one blank, the variable is still be 
set, so isset() will return true.  empty() will also return true as 
it's empty, even though it's set.  But also note that since PHP 4, if 
someone enters in the value 0 into a form, it's also seen as empty.
For a useful type comparisons chart of isset() vs empty() vs many other 
functions and syntax, see this appendix:
    http://www.php.net/manual/en/types.comparisons.php