c++ - 类中的typedef

Question

有这样的代码:

template <class T>
class SomeClass{
    typedef boost::shared_ptr<T> sPtr;
    typedef std::vector<sPtr> c;
    typedef c::iterator cIt;  // here is the problem
};

错误是:

main.cpp:23: error: type ‘std::vector<boost::shared_ptr<X>, std::allocator<boost::shared_ptr<X> > >’ is not derived from type ‘SomeClass<T>’
main.cpp:23: error: expected ‘;’ before ‘cIt’

如何在类中使用typedef来模板化参数？

编辑:

我想通了，对于 g++，那一定是:

typedef typename c::iterator cIt;  // here is the problem

请关闭它。

Answer 1

问题是 c::iterator 是一个 qualified-id，c 的类型取决于模板参数。根据 §14.6/3:

When a qualified-id is intended to refer to a type that is not a member of the current instantiation and its nested-name-specifier refers to a dependent type, it shall be prefixed by the keyword typename ...