isset
Description
bool isset ( mixed var [, mixed var [, ...]])Returns TRUE if var exists; FALSE otherwise.
If a variable has been unset with unset(), it will no longer be set. isset() will return FALSE if testing a variable that has been set to NULL. Also note that a NULL byte ("\0") is not equivalent to the PHP NULL constant.
Warning: isset() only works with variables as passing anything else will result in a parse error. For checking if constants are set use the defined() function.
<?php
$var = '';
// This will evaluate to &true; so the text will be printed.
if (isset($var)) {
print "This var is set set so I will print.";
}
// In the next examples we'll use var_dump to output
// the return value of isset().
$a = "test";
$b = "anothertest";
var_dump( isset($a) ); // TRUE
var_dump( isset ($a, $b) ); // TRUE
unset ($a);
var_dump( isset ($a) ); // FALSE
var_dump( isset ($a, $b) ); // FALSE
$foo = NULL;
var_dump( isset ($foo) ); // FALSE
?> |
This also work for elements in arrays:
<?php
$a = array ('test' => 1, 'hello' => NULL);
var_dump( isset ($a['test']) ); // TRUE
var_dump( isset ($a['foo']) ); // FALSE
var_dump( isset ($a['hello']) ); // FALSE
// The key 'hello' equals NULL so is considered unset
// If you want to check for NULL key values then try:
var_dump( array_key_exists('hello', $a) ); // TRUE
?> |
Note: Because this is a language construct and not a function, it cannot be called using variable functions
See also empty(), unset(), defined(), the type comparison tables, array_key_exists(), and the error control @ operator.