正确：
array( "a" => "1", ), ); foreach ($arr as $a => &$trdata) { $trdata['b'] = $trdata['a']; } var_dump($arr);?> 错误：
array( "a" => "1", ), ); foreach ($arr as $a => $trdata) { $trdata['b'] = $trdata['a']; } var_dump($arr);?>