Overriding static variables when subclassing

Question

I have a class, lets call it A, and within that class definition I have the following:

static QPainterPath *path;

Which is to say, I\'m dec

Answer 1

I know this question has been answered, but there is an other way to set the value of a similar static variable for multiple classes through a helper class and some template specialization.

It doesn't exactly answer the question since it is not connected with subclassing in any way, but I've encountered the same issue and I found a different solution I wanted to share.

Example :

template <typename T>
struct Helper {
  static QPainterPath* path;
  static void routine();
}

// Define default values
template <typename T> QPainterPath* Helper<T>::path = some_default_value;
template <typename T> void Helper<T>::routine { do_somehing(); }

class Derived {};

// Define specialized values for Derived
QPainterPath* Helper<Dervied>::path = some_other_value;
void Helper<Dervied>::routine { do_somehing_else(); }

int main(int argc, char** argv) {
  QPainterPath* path = Helper<Derived>::path;
  Helper<Derived>::routine();
  return 0;
}

Pros:

• clean, compile time initialization
• static access (no instantiation)
• you can declare specialized static functions too

Cons:

• no virtualization, you need the exact type to retrieve the information

Answer 2

I haven't tested this, but introducing a virtual function:

struct Base {

    void paint() {
         APath * p = getPath();
         // do something with p
    }

    virtual APath * getPath() {
         return myPath;
    }

    static APath * myPath;
};

struct Derived : public Base  {

    APath * getPath() {
         return myPath;
    }
    static APath * myPath;
};

may be what you want. Note you still have to define the two statics somewhere:

APath * Base::myPath = 0;
APath * Derived::myPath = 0;