Question

我正在尝试为不同大小的矩阵和向量创建模板类。对于我的Vector类，我重载了+ =和+运算符，以便能够添加两个相同长度的向量。如果长度不匹配，我希望编译器抛出错误。我想将多个mvc :: Vector对象（具有不同的长度）存储在std :: vector中。为此，我创建了一个基类mvc :: VectorBase，该基类继承了所有mvc :: Vector对象。现在我可以写

std::vector<std::unique_ptr<mvc::VectorBase>> vectorBuffer;

为了能够从vectorBuffer调用MyVector的成员函数，我为这些成员添加了纯虚函数，以便可以使用

vectorBuffer[0]->GetLength().

我的问题：我无法编写代码，因为VectorBase不知道运算符重载。

mvc::Vector<2> result = (*vectorBuffer[0]) + (*vectorBuffer[1]);

试图将运算符重载作为纯虚函数添加到mvc :: VectorBase无效，因为一个参数必须是mvc :: Vector模板类的模板参数，我不能在模板之外使用。

#include <vector>
#include <memory>

#define T float

namespace mvc
{
    class VectorBase
    {
    public:
        // virtual Vector operator+= (Vector<Tlength>& other) = 0;
        virtual int GetLength() const = 0;
    };

    template<int Tlength>
    class Vector : public VectorBase
    {
    private:
        T vec[Tlength];

    public:
        Vector operator+ (Vector<Tlength>& other)
        {
            for (int i = 0; i < Tlength; i++)
            {
                vec[i] += other.vec[i];
            }
            return *this;
        }

        int GetLength() const
        {
            return Tlength
        }
    }
}

int main()
{
    mvc::Vector<3> vec3_1;
    mvc::Vector<3> vec3_2;
    mvc::Vector<4> vec4_1;

    mvc::Vector<3> result = vec3_1 + vec3_2; // this line works properly 
    mvc::Vector<3> result = vec3_1 + vec4_1; //this line won´t compile (as expected)

    std::vector<std::unique_ptr<mvc::VectorBase>> vectorBuffer;

    vectorBuffer.push_back(std::make_unique<mvc::Vector<2>>());
    vectorBuffer.push_back(std::make_unique<mvc::Vector<2>>());

    mvc::Vector<2> result = (*vectorBuffer[0]) + (*vectorBuffer[1]); // <-- this is what i want to be able to do
}

如何实现所需的行为：只有在使用相同模板（Tlength相等）生成MyVector对象的情况下，vectorBuffer [0] + vectorBuffer [1]才有效

这已经可以用于MyVector的两个单独存储的实例。当我使用多态性将多个mvc :: Vector对象存储在同一std :: vector中时，它将失败。

编辑： 通过使用基类作为返回类型重载+运算符，我得到了请求的行为：

#include <vector>
#include <memory>
#include <iostream>

#define T float

namespace mvc
{
    class VectorBase
    {
    public:
        virtual VectorBase* operator+ (VectorBase& other) = 0;
        virtual int GetLength() const = 0;
        virtual T GetElem(int i) const = 0;
        virtual void Print() const = 0;
    };

    template<int Tlength>
    class Vector : public VectorBase
    {
    private:
        T vec[Tlength];

    public:
        Vector(T initValue)
        {
            for (int i = 0; i < Tlength; i++)
            {
                vec[i] = initValue;
            }
        }

        VectorBase* operator+ (VectorBase& other) override
        {
            if (other.GetLength() != Tlength)
            {
                std::cout << "[Error]: Argument dimensions mismatch. Program will terminate." << std::endl;
                std::cin.get();
                exit(-1);
            }

            //Vector<Tlength> tmpOther = dynamic_cast<Vector<Tlength>&>(other);

            for (int i = 0; i < Tlength; i++)
            {
                //vec[i] += tmpOther.vec[i];
                vec[i] += other.GetElem(i);
            }
            return this;
        }


        Vector<Tlength> operator+ (Vector<Tlength>& other)
        {
            for (int i = 0; i < Tlength; i++)
            {
                vec[i] += other.GetElem(i);
            }
            return *this;
        }

        int GetLength() const override
        {
            return Tlength;
        }

        T GetElem(int i) const override
        {
            return vec[i];
        }

        void Print() const override
        {
            for (int i = 0; i < Tlength; i++)
            {
                std::cout << " " << vec[i] << "\n";
            }
            std::cout << std::endl;
        }
    };
}

int main()
{
    /* without polymorphism */
    // vector1
    mvc::Vector<2> vec3_1 = mvc::Vector<2>(1.2f);
    vec3_1.Print();
    // vector2
    mvc::Vector<2> vec3_2 = mvc::Vector<2>(3.4f);
    vec3_2.Print();
    // vector2 = vector1 + vector2
    vec3_2 = vec3_1 + vec3_2;
    vec3_2.Print();

    /* with polymorphism */
    // vector buffer storing base class objects
    std::vector<mvc::VectorBase*> vectorBuffer;
    //vector1
    vectorBuffer.push_back(new mvc::Vector<3>(3.5f));
    vectorBuffer[0]->Print();
    //vector2
    vectorBuffer.push_back(new mvc::Vector<3>(2.8f));
    vectorBuffer[1]->Print();
    //vector2 = vector1 + vector2
    vectorBuffer[1] = *vectorBuffer[0] + *vectorBuffer[1];
    vectorBuffer[1]->Print();

    std::cin.get();

    for (unsigned int i = 0; i < vectorBuffer.size(); i++)
    {
        delete vectorBuffer[i];
    }
}

plus运算符被两次重载，以也支持“非逻辑变形”用法。（请参阅main内部的示例）

使用@Vikas Awadhiya的dynamic_cast解决方案来赞扬操作员+覆盖。这也有效。与当前使用虚拟吸气功能GetElem的解决方案相比，目前我不了解性能。

目前，我只能使它与原始指针一起使用。仍在研究unique_ptr解决方案。

感谢所有回复！

Answer 1

我在代码上所做的更改很少，

#include <iostream>
#include <vector>
#include <memory>

namespace mvc
{

class VectorBase
{
    public:
    virtual ~VectorBase(){}

    virtual VectorBase& operator+ ( VectorBase& other) = 0;
    virtual int GetLength() const = 0;
};

template<int length>
class Vector: public VectorBase
{
private:
    double vec[length];

public:
    Vector(): VectorBase(),
        vec{}
    {

    }

    VectorBase& operator+ ( VectorBase& other) override
    {
        Vector< length>& subOther = dynamic_cast< Vector< length>&>( other);

        for ( int i = 0; i < length; i++)
        {
            vec[i] += subOther.vec[ i];
        }
        return *this;
    }

    int GetLength() const
    {
        return length;
    }


};

}


int main()
{
    std::vector<std::unique_ptr<mvc::VectorBase>> vectorBuffer;

    vectorBuffer.push_back( std::make_unique<mvc::Vector< 2>>());
    vectorBuffer.push_back( std::make_unique<mvc::Vector< 2>>());

    mvc::Vector< 2> result = dynamic_cast< mvc::Vector< 2>&>( *vectorBuffer[ 0] + *vectorBuffer[ 1]);

    std::cout<< "result.length = "<< result.GetLength()<< std::endl;

}

输出：result.length = 2

Answer 2

您可以通过使虚拟operator+返回并接受基类来做到这一点：

class VectorBase
{
public:
    virtual int GetLength() const = 0;
    // We have to return a heap allocated object because the actual type and,
    // hence, its size is unknown
    virtual std::unique_ptr<VectorBase> operator+(VectorBase& other) = 0;
};

template<int Tlength>
class Vector: public VectorBase
{
private:
    // ...

    std::unique_ptr<VectorBase> operator+(VectorBase& other) override
    {
        if (other.GetLength() != Tlength)
            return nullptr; // or throw an exception if you want

        Vector result = *this + static_cast<Vector<Tlength>&>(other);
        // or "new Vector<Tlength>(result)" if your compiler doesn't support C++14
        return std::make_unique<Vector<Tlength>>(result);
    }

    // ...
};

将多态与operator +重载模板类一起使用。如何实现基类？

2 个答案: