为什么？关于PHP数组和php foreach循环

Question

  

可能重复：
  Why does PHP overwrite values when I iterate through this array twice (by reference, by value)

$arr=array('a','b','c');

foreach($arr as &$v){
    echo $v;
}

foreach($arr as $v){
    echo $v;
}

结果是abcabb，而不是abcabc，为什么？