Syntax
bool isset ( mixed var [, mixed var [, ...] ] )
Popis
Príkaz jazyka PHP
Determine whether a variable is set
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.
Príklady
<?php
$var =
'';
// This will evaluate to TRUE so the text will be printed.
if (isset($var)) {
echo "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
?>
Pozri aj
empty, unset, defined, array_key_exists