php - How to bind pdo values in foreach loop -

i have code written php (pdo) -> sql server. throws no error, won't return db. have tried running sql outputs in sql server management studio , works perfect. also, outputting parameters bind make sure looks , does. reason on execution binds preventing sql running properly. there wrong method? possible bind in array loops trying here? code below, in advance.

public function insertstaff( $table, $param ) {     $qstr = '';     foreach( $_post $k => $v )     {         if( $k == 'dummy' || $v == '' )         {             $qstr .= '';         }         else         {             $qstr .= '?,';         }     }     $qstr = rtrim( $qstr, ',' );     $sql = "insert ? ($qstr) values ($qstr)";     $stmt = $this->c->prepare( $sql );     //bind table     $stmt->bindvalue( 1, $table, pdo::param_str );                         $output = '';     $x = 2;     foreach( $_post $k => $v )     {         if( $k !== 'dummy' && $v !== '' )         {             $stmt->bindvalue( $x, $k, pdo::param_str );             $output .= '<hr>'.$x.' => '.$k;             $x++;         }     }     foreach( $_post $k => $v )     {         if( $k !== 'dummy' && $v !== '' )         {             $stmt->bindvalue( $x, $v, pdo::param_str );             $output .= '<hr>'.$x.' => '.$v;             $x++;         }     }     //return $output;     if( $stmt->execute() )     {         return 'success';     }     else     {         return 'fail';     } }