Question

我有一个带有静态成员的班级MotionDirection。该类的源代码如下。但我无法初始化类的静态成员，我可以得到原因。所以问题出在MotionDirection.cpp，请参阅注释以了解有关编译器错误的详细信息。

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。这是Android-NDK项目，我从cygwin控制台运行编译。

Answer 1

第一个错误

只需替换

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

与

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

注意MotionDirection*在变量名称之前键入：您需要为编译器提供类型。

第二个错误

您不能将表达式放在功能块之外。有两种方法可以做到“正确”：

1

让initStatics()返回值。
添加私有静态变量。
通过为其分配值initStatics()来初始化新的静态变量。

2

添加嵌套类。
在其构造函数中写入initStatics()的调用。
添加该嵌套类的私有静态变量。

为什么我不能初始化静态成员

1 个答案:

第一个错误

第二个错误