Question

I’m trying to overload a Sum function which accepts a [list or vector] start and end iterator as arguments. This compiler error is really confusing me. Relevant code is as follows:

template <typename T1, typename T2>
const double Sum(const typename T1::const_iterator& start_iter, const typename T2::const_iterator& end_iter)
{// overloaded function that calculates sum between two iterators
    typename T1::const_iterator iterator_begin = start_iter;
    typename T2::const_iterator iterator_end = end_iter;

    double my_sum = 0;

    for (iterator_begin; iterator_begin != iterator_end; iterator_begin++)
        my_sum += *iterator_begin;

    return my_sum;      
}

int main()
{

list<double> test_list(10,5.1);
cout << Sum(test_list.begin(), test_list.end()); // compiler errors here

}

I get the following compiler errors:

iterators.cpp(72): error C2783: ‘const double Sum(const
T1::const_iterator &,const T2::const_iterator &)’ : could not deduce
template argument for ‘T1’

iterators.cpp(72): error C2783: ‘const double Sum(const
T1::const_iterator &,const T2::const_iterator &)’ : could not deduce
template argument for ‘T2’

iterators.cpp(72): error C2780: ‘const double Sum(const
std::map &)’ : expects 1 arguments – 2 provided

iterators.cpp(72): error C2780: ‘const double Sum(const T &)’ :
expects 1 arguments – 2 provided

How is the compiler not recognizing I’m trying to call the Sum function with two inputs? I’m calling the function incorrectly?

Thanks!

Answer 1

You dont need to tell it that iterators have to be members of some types T1 and T2, just template it on iterator type itself:

template <typename Iter>
const double Sum(Iter iterator_begin, Iter iterator_end)
{
    double my_sum = 0;
    for (; iterator_begin != iterator_end; ++iterator_end)
        my_sum += *iterator_begin;
    return my_sum;      
}

int main()
{
    std::list<double> test_list;
    std::cout << Sum(test_list.begin(), test_list.end());
    return 0;
}

also there is a standard std::accumulate that does this:

int main()
{
    std::list<double> test_list;
    std::cout << std::accumulate(test_list.begin(), test_list.end(), 0.0);
    return 0;
}