c++ - Nested data member pointer - not possible?

Question

The following reduced code sample does not do anything useful but two subsequent assignments to a data member pointer. The first assignment works, the second one gives a compiler error. Presumably because its to a nested member.

Question would be: Is it really just not possible to let a member pointer point to a nested member or am I missing any fancy syntax there?

struct Color {
    float Red;
    float Green;
    float Blue; };


struct Material {
    float Brightness;
    Color DiffuseColor; };


int main() {
    float Material::* ParamToAnimate;
    ParamToAnimate = &Material::Brightness;       // Ok
    ParamToAnimate = &Material::DiffuseColor.Red; // Error! *whimper*
    return 0; }

ATM I am working around by using byte offsets and a lot of casts. But that is ugly, I would better like to use those member pointers.

Yes, I know that question surely arised before (like nearly any question). Yes, I searched beforehand but found no satisfying answer.

Thanks for your time.

Answer 1

I assume you are trying to get the pointer to the datamember Red. Since this is defined in the struct Color the type of the pointer is Color::*. Hence your code should be:

int main() {
    float Color::* ParamToAnimate;
    ParamToAnimate = &Color::Red; 
    return 0; }

To use it, you need to bind it to an instance of Color for example:

void f(Color* p, float Color::* pParam)
{
    p->*pParam = 10.0;
}
int main() {
    float Color::* ParamToAnimate;
    ParamToAnimate = &Color::Red; 

    Material m;
    f(&m.DiffuseColor, ParamToAnimate);
    return 0;
}

EDIT: Is it not possible to make the animation function a template? For example:

template<class T>
void f(T* p, float T::* pParam)
{
    p->*pParam = 10.0;
}
int main() {

    Material m;

    f(&m.DiffuseColor, &Color::Red);
    f(&m, &Material::Brightness);
    return 0;
}