PHP Functions Essential Reference

isset

bool isset(mixed variable) 

Tests whether a variable is set.

Returns:

TRUE if the variable contains a value other than NULL; FALSE otherwise

Description:

isset() is used to check whether a variable is currently set.

Note:

If the variable contains a null value (NULL), isset() returns FALSE. Note that a null byte ("\0") is not equivalent to the PHP constant NULL. If a variable contains only a null byte ("\0"), it is still considered to be set.

Also note that isset() cannot be used on a literal (such as 10, "A string", and so on)—see the example.

Availability:

UNIX, Windows

Version:

3+, 4+

See also:

empty() 

Example:

Demonstrate how isset() works

<pre> <?php $greeting = "Hi!"; if (isset ($value)) print "\$greeting is set.\n"; else print ...