c ++模板和迭代器

Question

I am trying to declare this function :

template <typename T> void hi(std::map<T,double> m,std::vector<std::map<T,double>::iterator > vec)
{
    //....
}

I want the function to have as parameters a map of and a vector of iterators on this map. But the g++ compiler does not seem to like it and I receive the following error :

 type/value mismatch at argument 1 in template parameter list for ‘template<class _Tp,     class _Alloc> class std::vector’
: error:   expected a type, got ‘std::map::iterator’
: error: template argument 2 is invalid

Any help please?

Answer 1

You must write typename before the iterator argument

template <typename T> 
void hi(std::map<T,double> m, std::vector<typename  std::map<T,double>::iterator > vec)
                                          ^^^^^^^^
{
    //....
}

Yes, it is unfortunate that typename has 2 different meanings. Some authors use template<class T> for precisely that reason, in order to visually disambiguate template parameter declarations from dependent type extraction. Especially in template-metaprogramming this can help to make code a bit more readable.