CODEWITHSUNDEEP
templatesinheritancec++11constructorclang++
fuenfundachtzig
fuenfundachtzig

Reputation: 8352

Constructor inheritance in templated class (C++11)

I have the following class definition:

template<typename T>
class Point {
  private:
    T px, py;
  public:
    Point(T x, T y): px(x), py(y) {
      std::cout << "created " << x << ":" << y <<std::endl;
    };
    T x() const { return px; };
    T y() const { return py; };
};

from which I am deriving specializations, e.g.

class PointScreen: public Point<int> {
  using Point::Point;
};

When I compile this in clang++, I get no warning / error, but the constructor is not called:

#include <iostream>
// definitions from above      
int main() {
  std::cout << PointScreen(100, 100).x() << std::endl;
  return 0;
}

This returns a random value (and also not the debug output "created..."). The value returned by e.g. x() is obviously "undefined".

I have just tried the same in g++ here, and there I obtain the expected result. Is this a problem with clang++ or have I a bug in my code?

My clang version: Ubuntu clang version 3.0-6ubuntu3 (tags/RELEASE_30/final) (based on LLVM 3.0). I compile with -std=c++11 -Wall.

Upvotes: 4

Views: 1222

Answers (1)

TemplateRex
TemplateRex

Reputation: 70506

As pointed out in the comments, you need a compiler supporting inheriting constructors. From the Apache C++11 overview you can see that this feature is only available for gcc >= 4.8 and Clang >= 3.3.

For older compilers, you have to manually define all the constructors, by calling the base constructors. See also this Q&A for more details on work-arounds.

Upvotes: 1

Related Questions