CODEWITHSUNDEEP
c++templates
Abby Jean
Abby Jean

Reputation: 113

Calling a template function from a template function in a class

I am trying to use a template function from a template function in a class. I have the following code in class Sort.h:

class Sort {
public:
    Sort();
    virtual ~Sort();
    template <typename T>
    static std::vector<T> merge (std::vector<T> array, int p, int q, int r);
    template <typename T>
    static std::vector<T> merge_sort(std::vector<T> array, bool ascending);
};

template <typename T>
std::vector<T> merge (std::vector<T> array, int p, int q, int r){
    std::vector<T> L = std::vector<T>(array.begin() + p, array.begin() + q + 1);
    std::vector<T> R = std::vector<T>(array.begin() + q + 1, array.begin() + r + 1);
    T max = std::numeric_limits<T>::max();
    L.push_back (max);
    R.push_back (max);
    int j, k = 0;
    for (int i = p; i <= r; i++){
        if (L[j] <= R[k]){
            array[i] = L[j];
            j++;
        } else {
            array[i] = R[k];
            k++;
        }
    }
    return array;
}


template <typename T>
std::vector<T> Sort::merge_sort(std::vector<T> array, bool ascending){
    array = Sort::merge<T>(array, 0, 4, 9); // some random numbers
    return array;
}

And then I try to use it in int main as:

std::vector<int> o = Sort::merge_sort<int>(input, 1);

where "input" is simply a vector of int type. But I get an error:

undefined reference to std::vector<int, std::allocator<int> > Sort::merge<int>(std::vector<int, std::allocator<int> >, int, int, int)

I don't know why the compiler is looking for an std::vector<int, std::allocator<int> > function, shouldn't it look for an std::vector<int> function instead? How can I make this work? Thank you!

Upvotes: 1

Views: 76

Answers (1)

jtbandes
jtbandes

Reputation: 118681

You have accidentally declared a separate function called merge that is not part of the Sort class.

Instead of

template <typename T>
std::vector<T> merge ( ...

you need:

template <typename T>
std::vector<T> Sort::merge ( ...

Upvotes: 2

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