Undefined reference of Composer class for Strategy pattern, C++ [duplicate]

I have the book "Design Patterns, Elements of Reusable Object-Oriented Software", and I've been using the internet. I've boiled down my code to bare minimum.

I don't know why I get the error messages:

Error    undefined reference to `InputStrategy::InputStrategy()'

I can post more of the error, but it was just the recipe for target failed, and the subsequent undefined reference being passed in to Input(new BinaryInputStrategy());

Does anyone see why this isn't working?

#include <avr/io.h>

class InputStrategy {
    protected:
        InputStrategy();
};

class Input {
    public:
        Input(InputStrategy* is) {
            inputStrategy = is;
        }
    private:
        InputStrategy *inputStrategy;
};

class BinaryInputStrategy : public InputStrategy {
    public:
        BinaryInputStrategy() {}
};

int main(void) { 
    Input ins = Input(new BinaryInputStrategy());
    while (1) {}
}