将字符串附加到输出

Question

I have following code in wordpress :

foreach($out as $outs)
{

    $store = $outs->store; 
    $latv = $outs->lat;
    $lngv = $outs->lng;
    $tagv = "#filter-list-".$outs->fax;


    $posts[] = array('latitude'=> $latv, 'longitude'=> $lngv, 'area'=>$tagv, 'content'=> $store);
}

I want to append #filter-list- .But the above code only output #filter-list-.It is not appending $outs->fax. I have tried variables of variables.But by doing this, it is taking null value.

So how can I append #filter-list- ?