stl中vector删除方法erase的原理

iterator erase(const_iterator _Where)
{    // erase element at where
_STDEXT unchecked_copy(_VEC_ITER_BASE(_Where) + 1, _Mylast,
_VEC_ITER_BASE(_Where));
_Destroy(_Mylast - 1, _Mylast);
--_Mylast;
return (_Make_iter(_Where));
}

stl:

iterator erase(iterator __position) {
if (__position + 1 != end())
copy(__position + 1, _M_finish, __position);
--_M_finish;
destroy(_M_finish);
return __position;
}