CODEWITHSUNDEEP
c++inheritancecompilation
Gilad
Gilad

Reputation: 6595

Define issue in C++ for derived classes

I have 2 Classes deriving from the same API, and want to be able to use the same API for both of them the only difference between the two is a define I need to put outside the API which will determine a something in the results returned by the joint function.

I'm having an issue with my design, I inherit this API and I can't change it.

Source.cpp

#include <fstream>
#include <vector>
#include "Version100.h"
#include "Version200.h"

int main()
{
    Version100* ver100 = new Version100();
    int res  = ver100->PlusOne(2);
    Version200* ver200 = new Version200();
    res  = ver200->PlusOne(2);
}

VersionAPI.h - this is the API I inherit I can't change this implementation

#pragma once
class VersionAPI
{
public:
    VersionAPI(void);
    ~VersionAPI(void);
    int PlusOne(int number);

};

VersionAPI.cpp - the problem I have is that I need to use different VERSION define for every class

#include "VersionAPI.h"


VersionAPI::VersionAPI(void)
{
}


VersionAPI::~VersionAPI(void)
{
}


int VersionAPI::PlusOne(int number)
{
    return number + VERSION;
}

Version100.h

#pragma once
#define VERSION 100 

#include "VersionAPI.h"


class Version100 :
    public VersionAPI
{
public:
    Version100(void);
    ~Version100(void);
};

Version100.cpp

#include "Version100.h"


Version100::Version100(void)
{
}


Version100::~Version100(void)
{
}

Version200.h

#pragma once

#define VERSION 200
#include "versionapi.h"
class Version200 :
    public VersionAPI
{
public:
    Version200(void);
    ~Version200(void);
};

Version200.cpp

#include "Version200.h"


Version200::Version200(void)
{
}


Version200::~Version200(void)
{
}

The error I'm getting is:

ersionapi.cpp(16): error C2065: 'VERSION' : undeclared identifier

I know this if because VERSION is defined outside the class.

Upvotes: 0

Views: 93

Answers (2)

juanchopanza
juanchopanza

Reputation: 227418

You can keep the public part of the API intact, and add a private virtual function that returns the version. The version itself can be a static member, which is different for each derived type, or just a value returned from the version() virtual function:

class VersionAPI
{
public:
    VersionAPI();
    virtual ~VersionAPI();        // Don't forget the virtual derstuctor!!!
    int PlusOne(int number) const // mark "final" in C++11 
    { 
      return version() + number;
    }

private:
    virtual int version() const { return 123; }
};

Then implement version() const in the derived types, returning the relevant version number.

class Version200 : public VersionAPI
{
public:
  Version200();
  ~Version200();
private:
  virtual int version() const { return 200; }
};

Upvotes: 1

NirMH
NirMH

Reputation: 4929

Define the VERSION as a member of each derived class and in the VersionApi make the PlusOne method virtual.

Upvotes: 1

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