c++ - 重写的虚函数没有被调用

Question

代码的更精确版本是:

class SomeParam;
class IBase
{
public:
    virtual void Func(SomeParam* param = NULL)
    {
        cout << "Base func";
    }
};

class DerivedA : public IBase
{
public:
    void Func()
    {
        //do some custom stuff
        cout << "DerivedA func";
        IBase::Func();
    }
};

class DerivedB : public IBase
{
public:
    void Func()
    {
        //do some custom stuff
        cout << "DerivedB func";
        IBase::Func();
    }
};

//at somewhere else
void FuncCaller(IBase *instance1, IBase *instance2)
{
    IBase *i1 = instance1;
    IBase *i2 = instance2;
    i1->Func();
    i2->Func();
}

DerivedA *a = new DerivedA;
DerivedB *b = new DerivedB;
FuncCaller(a,b);

这给了我:
“基础功能”
“基础功能”

Answer 1

看起来您提供了代码的简化版本以使其更具可读性，但您无意中过度简化了。

您的行为最可能的原因是:

• 在 FuncCaller() 中切片(有关详细信息，请参阅 quamrana 的回答)
• 错误的覆盖，比如派生类函数const，而基类函数不是const

编辑:阅读编辑后的问题后，显然是第二个原因。您并没有覆盖基类函数，而是将其隐藏在具有新定义的派生类中。您需要在派生类中保持完全相同的签名(协变在这里不适用，因为函数返回 void)。在代码中，您需要执行以下任一操作:

class SomeParam;
class IBase
{
public:
    virtual void Func(SomeParam* param = NULL)
    {
        cout << "Base func";
    }
};

class DerivedA : public IBase
{
public:
    void Func(SomeParam* param = NULL)
    {
        //do some custom stuff
        cout << "DerivedA func";
        IBase::Func();
    }
};

class DerivedB : public IBase
{
public:
    void Func(SomeParam* param = NULL)
    {
        //do some custom stuff
        cout << "DerivedB func";
        IBase::Func();
    }
};

//at somewhere else
void FuncCaller(IBase *instance1, IBase *instance2)
{
    IBase *i1 = instance1;
    IBase *i2 = instance2;
    i1->Func();
    i2->Func();
}

DerivedA *a = new DerivedA;
DerivedB *b = new DerivedB;
FuncCaller(a,b);

或

class SomeParam;
class IBase
{
public:
    virtual void Func()
    {
        cout << "Base func";
    }
};

class DerivedA : public IBase
{
public:
    void Func()
    {
        //do some custom stuff
        cout << "DerivedA func";
        IBase::Func();
    }
};

class DerivedB : public IBase
{
public:
    void Func()
    {
        //do some custom stuff
        cout << "DerivedB func";
        IBase::Func();
    }
};

//at somewhere else
void FuncCaller(IBase *instance1, IBase *instance2)
{
    IBase *i1 = instance1;
    IBase *i2 = instance2;
    i1->Func();
    i2->Func();
}

DerivedA *a = new DerivedA;
DerivedB *b = new DerivedB;
FuncCaller(a,b);