C ++派生类是抽象错误 [英] C++ Derived class is abstract error

问题描述

我有一个麻烦，在Dialin，派生类是抽象的。我不知道为什么，因为我唯一的虚拟函数，我有相同的参数和相同的返回类型。从我读过的，这是唯一的限制，但显然我错了。

I am having a trouble where Dialin, the derived class is abstract. I'm not sure why since the only virtual function I have has the same parameters and same return types. From what I've read, that's the only restriction, but apparently I'm wrong.

这是我的代码：

标题：

class Event{
    class ModemSimV2;

public:
    Event( );
    Event( const Event &e );
    ~Event( );

    virtual void process( ModemSimV2 &m ) = 0;

protected:
    int who;        // the number of the user
    int time;       // when the event will occur
    int what;       // DIAL_IN or HANGUP
};


 class Dialin : public Event{
     class ModemSimV2;
 public:
     Dialin( int name = 0, int tm = 0 );
     Dialin( const Dialin &d );
     ~Dialin( );

     virtual void process( ModemSimV2 &m );

 private:
     int who;
     int time;
     int what;
 };

---

来源：

---

Source:

Event::Event(){
}

Event::Event( const Event &e ) {
    *this = e;
}

Event::~Event( ) {
}

Dialin::Dialin (int name, int tm )
: time( tm ), who( name ) { 
    return;
}

Dialin::Dialin ( const Dialin &d ) {
    *this = d;
}

Dialin::~Dialin( ) {
}

void Dialin::process( ModemSimV2 &m ) {        
}

推荐答案

问题是有两种不同的转发声明 ModemSimV2 的类别：

The problem is that there are two different forward declarations of a class named ModemSimV2:

Event::ModemSimV2          // These are different classes
Dialin::ModemSimV2         // with the same unqualified name.

在事件 c $ c> process（）是：

In Event, the signature of process() is:

virtual void process( Event::ModemSimV2 &m ) = 0;

和 Dialin c $ c> process（）实际上是：

and in Dialin the definition of process() is actually:

virtual void process( Dialin::ModemSimV2 &m );

因此在 Event 未在 Dialin 中实现。

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