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isset

isset

Determine if a variable is declared and is different than null

bool **isset** mixed $var mixed $vars

Determine if a variable is considered set, this means if a variable is declared and is different than null.

If a variable has been unset with the function, it is no longer considered to be set. unset

will return false when checking a

variable that has been assigned to null. Also note that a null character () is not equivalent to the PHP null constant. isset``"\0"

If multiple parameters are supplied then will return true only if all of the parameters are considered set. Evaluation goes from left to right and stops as soon as an unset variable is encountered. isset

varThe variable to be checked.

varsFurther variables.

Returns true if exists and has any value other than null. false otherwise. var

Voorbeeld: Examples

<?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.", PHP_EOL;
}

// 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:

Voorbeeld: Example of with array elements

<?php

$a = array ('test' => 1, 'hello' => NULL, 'pie' => array('a' => 'apple'));

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

// Checking deeper array values
var_dump(isset($a['pie']['a']));        // TRUE
var_dump(isset($a['pie']['b']));        // FALSE
var_dump(isset($a['cake']['a']['b']));  // FALSE

?>

Voorbeeld: on String Offsets

<?php
$expected_array_got_string = 'somestring';
var_dump(isset($expected_array_got_string['some_key']));
var_dump(isset($expected_array_got_string[0]));
var_dump(isset($expected_array_got_string['0']));
var_dump(isset($expected_array_got_string[0.5]));
var_dump(isset($expected_array_got_string['0.5']));
var_dump(isset($expected_array_got_string['0 Mostel']));
?>

bool(false)
bool(true)
bool(true)
bool(true)
bool(false)
bool(false)

Waarschuwing: > only works with variables as passing anything else will result in a parse error. For checking if are set use the function. issetconstantsdefined

Opmerking: > When using on inaccessible object properties, the overloading method will be called, if declared. isset__isset()

empty__isset()unset``definedthe type comparison tablesarray_key_exists``is_null@

Vorige ← is_string Volgende print_r →

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