从Base类实例化Derived对象

Question

尝试创建一个驱动程序类型类,其中,Base是在实例化时传递类型的驱动程序.在这种情况下,类型2用于构造正确的派生对象.

我的编译器在"Class Base"行上抛出Declaration语法错误.

我的最终目标是能够做到这一点:

Base *B;

    B = new Base(2);
    if(B)
    {
      B->DoStuff();
      B->DoMoreStuff();
      delete B;
    }

这是我的代码,不会编译...

class Base
{
public:

    Base(int h);
    virtual ~Base();

private:
    int hType;
    Base *hHandle;
};


class Derived1 : public Base
{
public:
    Derived1();
    virtual ~Derived1();

};

class Derived2 : public Base
{
public:
    Derived2();
    virtual ~Derived2();

};

Base::Base(int h)
{
    hType = h;

    switch(h)
    {
        case 1:
            hHandle = new Derived1;
        break;

        case 2:
            hHandle = new Derived2;
        break;

    }
}


Derived1::Derived1():Base(1)
{
    printf("\nDerived1 Initialized\n\n");
}

Derived2::Derived2():Base(2)
{
    printf("\nDerived2 Initialized\n\n");
}

下面是更新的代码以显示完整的源代码.我想我现在明白为什么它不会编译.正如下面所指出的,我对"新"的调用无限循环

#include <stdio.h>

class Base
{
public:

    Base();
    Base(int h);
    Create (int h);
    virtual ~Base();

private:
    int hType;
    Base *hHandle;
};


class Derived1 : public Base
{
public:
    Derived1();
    virtual ~Derived1();

};

class Derived2 : public Base
{
public:
    Derived2();
    virtual ~Derived2();

};

Base::Base()
{

}

Base::Base(int h)
{
    Create(h);
}

Base::Create(int h)
{
    hType = h;

    switch(h)
    {
        case 1:
            hHandle = new Derived1;
        break;

        case 2:
            hHandle = new Derived2;
        break;

    }
}

Derived1::Derived1()
{
    printf("\nDerived1 Initialized\n\n");
}

Derived2::Derived2()
{
    printf("\nDerived2 Initialized\n\n");
}

Answer 1

看起来你正在尝试做一个类工厂。

我建议您在 Base 中有一个返回 Derived1 或 Derived2 的静态方法。

class Base
{
public:
    static Base* Create(int);
    virtual void DoStuff() = 0;
}

class Derived1 : public Base
{
    Derived1()
    {
        printf("\nDerived1 Initialized\n\n");
    }

    virtual void DoStuff()
    {
    }   
}

class Derived2 : public Base
{
    Derived2()
    {
        printf("\nDerived2 Initialized\n\n");
    }

    virtual void DoStuff()
    {
    }   
}

Base* Base::Create(int n)
{
    if (n==1)
        return new Derived1();
    else if (n==2)
        return new Derived2();
    else
        return nullptr;
}

void main()
{
    Base* B = Base::Create(2);
    if(B)
    {
        B->DoStuff();
        delete B;
    }
}