PHP: Check if variable exist but also if has a value equal to something

Question

I have (or not) a variable $_GET['myvar'] coming from my query string and I want to check if this variable exists and also if the value corresponds to something inside my if statement:

What I'm doing and think is not the best way to do:

if(isset($_GET['myvar']) && $_GET['myvar'] == 'something'): do something

My question is, exist any way to do this without declare the variable twice?

That is a simple case but imagine have to compare many of this $myvar variables.

Answer 1

Sadly that's the only way to do it. But there are approaches for dealing with larger arrays. For instance something like this:

$required = array('myvar', 'foo', 'bar', 'baz'); $missing = array_diff($required, array_keys($_GET)); 

The variable $missing now contains a list of values that are required, but missing from the $_GET array. You can use the $missing array to display a message to the visitor.

Or you can use something like that:

$required = array('myvar', 'foo', 'bar', 'baz'); $missing = array_diff($required, array_keys($_GET)); foreach($missing as $m ) {     $_GET[$m] = null; } 

Now each required element at least has a default value. You can now use if($_GET['myvar'] == 'something') without worrying that the key isn't set.

Update

One other way to clean up the code would be using a function that checks if the value is set.

function getValue($key) {     if (!isset($_GET[$key])) {         return false;     }     return $_GET[$key]; }  if (getValue('myvar') == 'something') {     // Do something } 

Answer 2

As of PHP7 you can use the Null Coalescing Operator ?? to avoid the double reference:

// $_GET['myvar'] isn't set...
echo ($_GET['myvar'] ?? '') == 'hello' ? "hello!\n" : "goodbye!\n";

// $_GET['myvar'] is set but != 'hello'
$_GET['myvar'] = 'farewell';
echo ($_GET['myvar'] ?? '') == 'hello' ? "hello!\n" : "goodbye!\n";

// $_GET['myvar'] is set and == 'hello'
$_GET['myvar'] = 'hello';
echo ($_GET['myvar'] ?? '') == 'hello' ? "hello!\n" : "goodbye!\n";

Output:

goodbye!
goodbye!
hello!

Code demo on 3v4l.org

In general, the expression

$a ?? $b

is equivalent to

isset($a) ? $a : $b

Note that in the code example it is necessary to place parentheses around $_GET['myvar'] ?? '' as == has higher precedence than ?? and thus

$_GET['myvar'] ?? '' == 'hello'

would evaluate to:

$_GET['myvar'] ?? ('' == 'hello')

which would be true as long as $_GET['myvar'] was set and "truthy" (see the manual) and false otherwise (since '' == 'hello' is false).

Precedence code demo on 3v4l.org