PHP将变量数组设置为空白

I am using these variables in my site:

$_SESSION["domain.com"]["var1"]
$_SESSION["domain.com"]["var2"]
$_SESSION["domain.com"]["var3"]

and so on... how can i set all of these variables to a certain value at once?

Are you just trying to set them all at the same time? Just set ['domain.com'] to an array.

$_SESSION['domain.com'] = array(
    'var1' => 'one',
    'var2' => 'two',
    'var3' => 'three',
);

Write a simple nested loop:

foreach ($_SESSION as &$vars) {
    foreach ($vars as &$value) {
        $value = $default_value;
    }
}

I use reference variables so the loop can modify the elements directly, instead of having to assign to $_SESSION[$domain][$variable].

Here is some sample code to get you up and running:

$variables=[];
$setTo=1;
foreach($_SESSION['domain.com'] as $key=>$v){
    $variables[]=$key;
}
$prefix='$_SESSION["domain.com"]["';
$eval=$prefix.implode('"]='.$prefix,$variables).'"]='.$setTo.";";
eval($eval);

Perfect for production use.