将不同类对象指针存放QVector中

需求：将一系列操作步骤放在链表中按需调用。

我将每个操作步骤用一个类实现，将各类继承于一个基类，再将指向各子类的基类指针放在QVector/Vector，即可通过C++的多态实现调用各子类。

为此，我写了俩个范例测试代码.

一，各子类只单一继承同一基类

#include <iostream>
#include <vector>
using namespace std;
#include <QDebug>

class Base
{
public:
    virtual ~Base() {}
    virtual void printName();
};

void Base::printName()
{}

class Derived0 : public Base
{
public:
    ~Derived0();
    void printName();
};

Derived0::~Derived0()
{}

void Derived0::printName()
{
    qDebug() << "I am derived 0";
}

class Derived1 : public Base
{
public:
    ~Derived1();
    void printName();
};

Derived1::~Derived1()
{}

void Derived1::printName()
{
    qDebug() << "I am derived 1";
}

int main()
{
    QVector<Base*> classVector;

    Base* ptrDerived0 = new Derived0;
    classVector.push_back(ptrDerived0);

    Base* ptrDerived1 = new Derived1;
    classVector.push_back(ptrDerived1);

    QVector<Base*>::iterator end = classVector.end();
    for (QVector<Base*>::iterator it = classVector.begin(); it != end; ++it) {
        (*it)->printName();
    }

    system("pause");
    return 0;
}

注意点：

基类Base， 虽简单，注意点还不少，如下错误：

class Base                                                 //这样将出现两个警告错误
{                                                  //1，“Base" has virtual functions but non-virtual destructor Base有虚函数，却用了非虚析构函数
public:                              //2，Base‘ has no out-of-line virtual method definitions；its vtable will be emitted in every translation unit.
    virtual void printName() = 0;           //base没有类外部虚方法定义，它的虚方法表会给每个翻译单元发送消息
};

1，任何有一个虚拟方法及打算使用多态方法的C++基类，都必须包含一个虚析构函数。这有助于确保当利用基类的指针访问子类（多态）时，可调用子类的析构函数，避免内存泄露。可是，出现这种常见的C++编译错误时，大多数C++编译器并没有警示信息。感谢QT 的警示信息！

因此，加上 virtual ~Base() {}

2，网摘：  If a class is defined in a header file and has a vtable (either it has virtual methods or it derives from classes with virtual methods), it must always have at least one out-of-line virtual method in the class. Without this, the compiler will copy the vtable and RTTI into every .o file that #includes the header, bloating .o file sizes and increasing link times
译：如果一个类在头文件中定义，并且有一个虚方法表（不管是虚方法还是继承基类的虚方法），那么该类必须至少将一个虚方法定义在类定义外部。否则，编译器将会复制虚表和RTTI给每一个包含该头文件的目标.o文件，折将膨涨.o文件的大小，增加编译连接时间。

因此，将纯虚函数声明在类内部：virtual void printName();

在类定义外部：viod Base::printName(){}

后面就是两个子类Derived0,Derived1继承Base，并将指向他们的Base指针加入Vector了。

运行结果是正常的

I am derived 0
I am derived 1

二  各基类除了继承这个统一基类以外，还继承别的类。 多继承，因为我各个步骤类还都继承别的类，如QDialog等等

#include <iostream>
#include <vector>
using namespace std;
#include <QDebug>

enum classType{BaseType,Derived0Type,Derived1Type};

class Base
{
public:
    virtual ~Base() {}
    virtual void printName() = 0;
    virtual classType myTypeNum();
};

classType Base::myTypeNum()
{
    return BaseType;
}

class Base1
{
public:
    void printBelong();
};

void Base1::printBelong()
{
    qDebug() << "I derived from Base1 too!";
}

class Derived0 : public Base, public Base1
{
public:
    ~Derived0();
    classType myTypeNum();
    void printName();
};

Derived0::~Derived0()
{}

classType Derived0::myTypeNum()
{
    return Derived0Type;
}

void Derived0::printName()
{
    qDebug() << "I am derived 0";
}

class Derived1 : public Base, public Base1
{
public:
    ~Derived1();
    classType myTypeNum();
    void printName();
};

Derived1::~Derived1()
{}

classType Derived1::myTypeNum()
{
    return Derived1Type;
}

void Derived1::printName()
{
    qDebug() << "I am derived 1";
}

int main()
{
    QVector<Base*> classVector;

    Base* ptrDerived0 = new Derived0;
    classVector.push_back(ptrDerived0);

    Base* ptrDerived1 = new Derived1;
    classVector.push_back(ptrDerived1);

    QVector<Base*>::iterator end = classVector.end();
    for (QVector<Base*>::iterator it = classVector.begin(); it != end; ++it) {
        if((*it)->myTypeNum() == Derived0Type)
        {
            dynamic_cast<Derived0*>((*it))->printName();
            dynamic_cast<Derived0*>((*it))->printBelong();
        }
        else if((*it)->myTypeNum() == Derived1Type){
            dynamic_cast<Derived1*>((*it))->printName();
            dynamic_cast<Derived1*>((*it))->printBelong();
        }
    }

    system("pause");
    return 0;
}

这里，我设计了一个专门定义各类返回类型的枚举类型enum classType{BaseType,Derived0Type,Derived1Type};

基类Base中设计为虚方法，返回BaseType；Derived0返回Derived0Type；Derived1返回Derived1Type。

子类除了继承Base以外，还继承Base1.

那么为了子类能正常调用不同基类的虚方法，要将Vector中统一的Base指针转换为自己的指针，这里就需要上面classType帮助判断了。如

if((*it)->myTypeNum() == Derived0Type)
        {
            dynamic_cast<Derived0*>((*it))->printName();
            dynamic_cast<Derived0*>((*it))->printBelong();
        }

运行结果也是如我所愿的

I am derived 0
I derived from Base1 too!
I am derived 1
I derived from Base1 too!