类指针作为另一个对象的数据成员

Question

just getting an odd error and I'm not entirely sure as to why.

I have 4 files (two headers and two implementations). The issue is inside the headers:

The main file ONLY includes the Station.h, which is why Stations.h is included inside it.

Station.h

#ifndef STATION_H
#define STATION_H
#include "Stations.h"

#include <string>

enum PassType{student, adult};

class Station{

        std::string station_name;
        unsigned int student_passes;
        unsigned int adult_passes;

    public:
        Station();
        void set(const std::string&, unsigned, unsigned);
        void update(PassType, int);
        unsigned inStock(PassType) const;
        const std::string& getName() const;

};


#endif

Stations.h

#ifndef STATIONS_H
#define STATIONS_H
#include "Station.h"

namespace w2{

    class Stations{

    Station *station;

    public:
        Stations(char *);
        void update() const;
        void restock() const;
        void report() const;
        ~Stations();

    };

}

#endif

It doesn't know what Station is. I'm getting the following error:

./Stations.h:9:2: error: unknown type name 'Station'; did you mean 'Stations'?
        Station *station;

What exactly am I missing here?

Answer 1

Don't forget to put a semicolon after you declare the Stations class:

class Stations {
     Station *station;
};

Answer 2

U need to do the forward declaration. Remove the #include "Stations.h" from the Station.h

#ifndef STATIONS_H
#define STATIONS_H
#include "Station.h"

namespace w2{
    class Station;
    class Stations{

    Station *station;

    public:
        Stations(char *);
        void update() const;
        void restock() const;
        void report() const;
        ~Stations();

    };

}

#endif

Answer 3

You are #include ing Stations.h in Station.h. As a result, the compiler sees class Stations before class Station . In this case, it doesn't appear that Station requires Stations , so you can simply remove the include.

If Station did need to know about Stations , then you'd have to use a forward declaration in one of the headers or the other (and be careful not to use the forward-declared class in a way that required the full definition).