#include <iostream>
#include <string>
#include <vector>

struct Feature {
  float x;
  float y;
  float value;
};

class BaseClass {
  public:
    int GetDetections(const std::string& filename) const {
        // Normally, I'd read in features from a file, but for this online
        // example, I'll just construct an feature set manually.
        std::vector<Feature> features;
        return GetDetections(features);
    };
    // Pure virtual function.
    virtual int GetDetections(const std::vector<Feature>& features) const = 0;
};

class SubClass : public BaseClass {
  public:
    // Giving the pure virtual function an implementation in this class.
    int GetDetections(const std::vector<Feature>& features) const {
        return 7;
    }
};

int main() {
    SubClass s;
    std::cout << s.GetDetections("testfile.txt");
}