isset

(PHP 3, PHP 4, PHP 5 )isset -- Determine whether a variable is set

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)) {
 echo "This var is 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

?>

<?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 ?> Замечание: Поскольку это языковая конструкция, а не функция, она не может вызываться при помощи переменных функций