PHP 忒聊 綴豖 ヶ輛 isset (PHP 3, PHP 4) Description 蛁: isset() is a language construct. Returns TRUE if var exists; FALSE otherwise. If a variable has been unset with unset(), it will no longer be isset(). 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? See also empty(), unset(), defined(), array_key_exists() and the error control @ operator. 綴豖 れ萸 ヶ輛 is_string 奻珨撰 print_r