Check If Value Isset and Null

Check if value isset and null

IIRC, you can use get_defined_vars() for this:

$foo = NULL;
$vars = get_defined_vars();
if (array_key_exists('bar', $vars)) {}; // Should evaluate to FALSE
if (array_key_exists('foo', $vars)) {}; // Should evaluate to TRUE

PHP check if False or Null

For returns from functions, you use neither isset nor empty, since those only work on variables and are simply there to test for possibly non-existing variables without triggering errors.

For function returns checking for the existence of variables is pointless, so just do:

if (!my_function()) {
    // function returned a falsey value
}

To read about this in more detail, see The Definitive Guide To PHP's isset And empty.

Are isset() and !== null equivalent?

From PHP Manual:

isset — Determine if a variable is set and is not NULL

isset Returns TRUE if var exists and has value other than NULL, FALSE otherwise.

http://php.net/manual/en/function.isset.php

The function call overhead is so small you probably don't need to worry about it.
Read this post: Why are PHP function calls *so* expensive?

Note that isset is not a function (it has a special opcode for it), so it's faster.

Check if array value isset and is null

Use array_key_exists() instead of isset(), because isset() will return false if the variable is null, whereas array_key_exists() just checks if the key exists in the array:

function check($array, $key)
{
    if(array_key_exists($key, $array)) {
        if (is_null($array[$key])) {
            echo $key . ' is null';
        } else {
            echo $key . ' is set';
        }
    }
}

Will isset() return false if I assign NULL to a variable?

bool isset ( mixed $var [, mixed $var [, $... ]] )

Determine if a variable is set and is not NULL.

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.

Return values

Returns TRUE if var exists and has value other than NULL, FALSE otherwise.

From the manual. Examples on the same page.

In where shall I use isset() and !empty()

isset vs. !empty

FTA:

"isset() checks if a variable has a
value including (False, 0 or empty
string), but not NULL. Returns TRUE
if var exists; FALSE otherwise.

On the other hand the empty() function
checks if the variable has an empty
value empty string, 0, NULL or
False. Returns FALSE if var has a
non-empty and non-zero value."

Check for multiple null isset values

For that you can use relational operators. AND (&&) OR (||)

By using AND (&&) operators.

if ( (!isset($myarray['dataone']) || (!isset$myarray['datatwo'] ))
{
    echo 'false';  
} 
else 
{
    echo 'true';
}

By using OR ( || ) operators.

if (isset($myarray['dataone'] && isset$myarray['datatwo'])
{
    echo 'false';  
} 
else 
{
    echo 'true';
}

Why check both isset() and !empty()

This is completely redundant. empty is more or less shorthand for !isset($foo) || !$foo, and !empty is analogous to isset($foo) && $foo. I.e. empty does the reverse thing of isset plus an additional check for the truthiness of a value.

Or in other words, empty is the same as !$foo, but doesn't throw warnings if the variable doesn't exist. That's the main point of this function: do a boolean comparison without worrying about the variable being set.

The manual puts it like this:

empty() is the opposite of (boolean) var, except that no warning is generated when the variable is not set.

You can simply use !empty($vars[1]) here.

isset($_GET(var)) is true even if var is null or undefined

A sample code show difference between isset and empty

<?php
$a = array('blank'=>'');
var_dump(isset($a['blank']));  // bool(true)
var_dump(!empty($a['blank'])); // bool(false)

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