Question

I have a class MotionDirection with static members. The source code of the class is below. But I just can not initialize the static members of the class and I can get the reason. So the problem is in the MotionDirection.cpp, see the comments for the details about the compiler errors.

MotionDirection.h

#ifndef MOTION_DIRECTION
#define MOTION_DIRECTION

namespace game{
    class IntPosition;

    class MotionDirection {
        private:
        IntPosition* positionDisplacement;
        float angle;
        MotionDirection* returnDirection;

        public:
        MotionDirection( IntPosition* positionDisplacement, float angle );
        void setReturnDirection ( MotionDirection* returnDirection );

        IntPosition* getPositionDisplacement();
        float getAngle();
        MotionDirection* getReturnDirection();

        static MotionDirection* NONE;
        static MotionDirection* LEFT;
        static MotionDirection* RIGHT;
        static MotionDirection* UP;
        static MotionDirection* DOWN;

        static void initStatics();
    };
}

#endif 

MotionDirection.cpp

#include "MotionDirection.h"
#include "IntPosition.h"

namespace game{
    MotionDirection::NONE = new MotionDirection ( new IntPosition( 0, 0),   0.0f );
    // here I get an error:
    // MotionDirection.cpp:10:5: error: 'NONE' in 'class game::MotionDirection' does not name a type

    MotionDirection::MotionDirection( IntPosition* positionDisplacement, float angle ) {
        this->positionDisplacement = positionDisplacement;
        this->angle = angle;
    }

    void MotionDirection::setReturnDirection ( MotionDirection* returnDirection ) {
        this->returnDirection = returnDirection;
    }

    IntPosition* MotionDirection::getPositionDisplacement() {
        return positionDisplacement;
    }

    float MotionDirection::getAngle() {
        return angle;
    }

    MotionDirection* MotionDirection::getReturnDirection() {
        return returnDirection;
    }

    void MotionDirection::initStatics () {
        MotionDirection::NONE  = new MotionDirection ( new IntPosition( 0, 0),   0.0f );
        MotionDirection::LEFT  = new MotionDirection ( new IntPosition(-1, 0), 180.0f );
        MotionDirection::RIGHT = new MotionDirection ( new IntPosition( 1, 0),   0.0f );
        MotionDirection::UP    = new MotionDirection ( new IntPosition( 0,-1),  90.0f );
        MotionDirection::DOWN  = new MotionDirection ( new IntPosition( 0, 1), 270.0f );
    }

    MotionDirection::initStatics();
    // or here I get an error:
    // MotionDirection.cpp:45:35: error: expected constructor, destructor, or type conversion before ';' token

}

P.S. This is Android-NDK project, I run compilation from the cygwin console.

Answer 1

First error

Just replace

MotionDirection::NONE = new MotionDirection ( new IntPosition( 0, 0),   0.0f );

with

MotionDirection* MotionDirection::NONE = new MotionDirection ( new IntPosition( 0, 0),   0.0f );

Note MotionDirection* type before name of the variable: you need to provide compiler with a type.

Second error

You can’t put expressions out of function blocks. There are two ways to do this “right”:

1.

• Make initStatics() return value.
• Add private static variable.
• Initialize new static variable by assigning value of initStatics() to it.

2.

• Add nested class.
• Write call to initStatics() in its constructor.
• Add private static variable of that nested class.