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Where and why do I have to put the “template” and “typename” keywords?
本文转自Stroustroup's FAQ .我见过当您不知道类型时使用的类型名称，例如在模板中，template <typename> class some_class .为什么在下面的示例中使用 typename？
template<class T> void printall(const vector<T>& v)
{
for (auto p = v.begin(); p!=v.end(); ++p)
cout << *p << "\n";
}
In C++98, we'd have to write
template<class T> void printall(const vector<T>& v)
{
for (typename vector<T>::const_iterator p = v.begin(); p!=v.end(); ++p)
cout << *p << "\n";
}