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 somethi

Answer 1

As mellowsoon suggest, you might consider this approach:

required = array('myvar' => "defaultValue1", 'foo' => "value2", 'bar' => "value3", 'baz' => "value4");
$missing = array_diff($required, array_keys($_GET));
foreach($missing as $key => $default  ) {
    $_GET[$key] = $default  ;
}

You put the default values and set the not recieved parameters to a default value :)

Answer 2

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

$_GET['myvar'] = 'hello';
if (($_GET['myvar'] ?? '') == 'hello') {
    echo "hello!";
}

Output:

hello!

In general, the expression

$a ?? $b

is equivalent to

isset($a) ? $a : $b

Answer 3

I use all time own useful function exst() which automatically declare variables.

Example -

$element1 = exst($arr["key1"]);
$val2 = exst($_POST["key2"], 'novalue');


/** 
 * Function exst() - Checks if the variable has been set 
 * (copy/paste it in any place of your code)
 * 
 * If the variable is set and not empty returns the variable (no transformation)
 * If the variable is not set or empty, returns the $default value
 *
 * @param  mixed $var
 * @param  mixed $default
 * 
 * @return mixed 
 */

function exst( & $var, $default = "")
{
    $t = "";
    if ( !isset($var)  || !$var ) {
        if (isset($default) && $default != "") $t = $default;
    }
    else  {  
        $t = $var;
    }
    if (is_string($t)) $t = trim($t);
    return $t;
}

Answer 4

Thanks Mellowsoon and Pekka, I did some research here and come up with this:

• Check and declare each variable as null (if is the case) before start to use (as recommended):

!isset($_GET['myvar']) ? $_GET['myvar'] = 0:0;

*ok this one is simple but works fine, you can start to use the variable everywhere after this line

• Using array to cover all cases:

$myvars = array( 'var1', 'var2', 'var3');
foreach($myvars as $key)
    !isset($_GET[$key]) ? $_GET[$key] =0:0;

*after that you are free to use your variables (var1, var2, var3 ... etc),

PS.: function receiving a JSON object should be better (or a simple string with separator for explode/implode);

... Better approaches are welcome :)

---

UPDATE:

Use $_REQUEST instead of $_GET, this way you cover both $_GET and $_POST variables.

!isset($_REQUEST[$key]) ? $_REQUEST[$key] =0:0;

Answer 5

A solution that I have found from playing around is to do:

if($x=&$_GET["myvar"] == "something")
{
    // do stuff with $x
}

Answer 6

This is similar to the accepted answer, but uses in_array instead. I prefer to use empty() in this situation. I also suggest using the new shorthand array declaration which is available in PHP 5.4.0+.

$allowed = ["something","nothing"];
if(!empty($_GET['myvar']) && in_array($_GET['myvar'],$allowed)){..}

Here is a function for checking multiple values at once.

$arrKeys = array_keys($_GET);
$allowed = ["something","nothing"];

function checkGet($arrKeys,$allowed) { 
    foreach($arrKeys as $key ) {
        if(in_array($_GET[$key],$allowed)) {
            $values[$key];
        }
    }
    return $values;
}