Calling a constructor of a class, inherited by multiple classes - c++

Question

Straight to the point:
I've got 2 classes. One stores one set of information, another - different information.
.h file
class Direction
{
private:
std::vector<float> dir;
public:
Direction(std::vector<float> objDir); ......};
.cpp file
#ifndef frw_dir_ed
#define frw_dir_ed
#include "frw_direction.h"
#endif
FRW::Direction::Direction(std::vector<float> objDir = { .0f, .0f })
{
for (int i = 0; i < 2; i++)
dir[i] = objDir[i];
}
Direction(float x, float y);
Another .h file:
class Position
{
private:
float posX;
float posY;
public:
Position(float x, float y);
Another .cpp file:
#ifndef frw_pos_ed
#define frw_pos_ed
#include "frw_position.h"
#endif // !frw_pos_ed
FRW::Position::Position(float x = 0, float y = 0)
{
setPos(x, y);
}
I also have a third class. This one inherits 2 previous.
class gameObj : public Position, public Direction
{
public:
gameObj(float x, float y, std::vector<float> direction, bool renderable);
gameObj(float posX, float posY, float dirX, float dirY, bool renderable);
//some funcs, destructor
private:
FRW::Position objPos;
FRW::Direction objDir;
bool isRendered;
};
That was a header file, now .cpp:
FRW::gameObj::gameObj(float x = 0.5f, float y = 0.5f, std::vector<float> direction = { .0f, .0f }, bool renderable = true)
: FRW::Direction::Direction(direction), FRW::Position::Position(x,y)
{
isRendered = renderable;
}
FRW::gameObj::gameObj(float posX = 0.5f, float posY = 0.5f, float dirX = .0f, float dirY = 0.f, bool renderable = true)
: FRW::Direction::Direction(dirX, dirY), FRW::Position::Position(posX, posY)
{
isRendered = renderable;
}
C2456 compiler error: member function or nested class in costructor initializer list
Error 3 error C2535: 'void FRW::gameObj::__dflt_ctor_closure(void)' : member function already defined or declared.
Please, can anyone tell me, which concept of OOP I missed? Why I am getting this error?

Answer 1

You either need to inherit from a class or have an element of that type as a member, not both! i.e. this:
class gameObj
{
public:
// ...
private:
FRW::Position objPos;
FRW::Direction objDir;
bool isRendered;
};
or this:
class gameObj : public Position, public Direction
{
public:
// ...
private:
bool isRendered;
};
but not this:
class gameObj : public Position, public Direction
{
public:
// ...
private:
FRW::Position objPos;
FRW::Direction objDir;
bool isRendered;
};
(Actually it's possible you'd want the last one, but very rare in practice.) With the last one, you end up with two directions in gameObj: the gameObj::objDir member, and the direction that the gameObj inherits from. In this case you probably want the member variable (a person has a direction, but it's not true that a person is a direction).This is called using composition rather than inheritance, and it's usually best if you can get away with it. As guide, you normally shouldn't use inheritance unless you need virtual functions. The reason for the compilation error is that you're only initialising one of those two directions (and one of the two positions).
By the way, the error would have been hidden by the fact that you have default values for the constructors. But they need to be in the header than the .cpp (otherwise only code in the .cpp after the definitions will "know" about the defaults).
Edit: Additionally, the code FRW::Direction::Direction(dirX, dirY) should be FRW::Direction(dirX, dirY). This is the real cause of the compilation error (but once you fix it I think you'll get the error I mention above).