$first ="hello";
$hello ="world";
echo $first." ".$$first;
结果是 hello world
$$first就是$hello,因为$first的值是hello
http://www.php.net/manual/zh/language.variables.variable.php
$first ="hello";
$hello ="world";
echo $first." ".$$first;
结果是 hello world
$$first就是$hello,因为$first的值是hello
http://www.php.net/manual/zh/language.variables.variable.php