Bdtjtk

I got this:

class Core

{

protected:

    static unsigned int id_seed;

    unsigned int id;

    std::string status;



public:

    friend class CPU;

    Core();

    ~Core();



    virtual void procesare(std::string aplicatie) = 0;

};





class CoreScreen: public Core

{

public:

    CoreScreen();

    ~CoreScreen();



    void procesare(std::string aplicatie);

};

and corescreen.cpp:

#include "CoreScreen.h"



CoreScreen::CoreScreen()

{

}



CoreScreen::~CoreScreen()

{

}



void CoreScreen::procesare(std::string aplicatie)

{

    std::string buffer;

    std::ifstream file_in(aplicatie);

    if (file_in.is_open()) {

        std::cout << "Aplicatia " << aplicatie << " ruleaza: " << std::endl;

        while (getline(file_in, buffer)) {

            std::cout << buffer;

        }

        file_in.close();

    }

    else {

        throw new CExceptie(APP_FAIL, " Aplicatia nu a putut rula!");

    }

}

When I use in main:

CoreScreen CS1, CS2, CS3, CS4;

I get this error: 'Core' cannot instantiate abstract class.

What's the problem? I thought I have my virtual function declared in CoreScreen correctly.

As I presume you know, "Core" is an abstract class, by virtue of the fact it has a pure virtual function: virtual void procesare(std::string aplicatie) = 0;.

I presume you also know that you can't instantiate an abstract class: hence your error.

The question is:

Why does the compiler think you're trying to instantiate an instance of "Core"?

Are you?

It looks like you're trying to instantiate four CoreScreen objects: CoreScreen CS1, CS2, CS3, CS4;. If so, that should be perfectly OK.

You're correct: procesare() is virtual ("pure virtual", as it happens). You've indeed overridden it correctly in CoreScreen.cpp: it DOESN'T look like that's the problem.

Q: Did you ever implement Core::Core() and Core::~Core() anywhere? If not, how did you even compile?

Q: Are you SURE you're not trying to create an instance of "Core" anywhere (even "accidentally")?

For whatever it's worth, the following MCVE compiles and runs fine (Ubuntu 18, GCC 7.3.0):

TestCore.h:

/*

 * TestCore.h

 */

#ifndef TESTCORE_H_

#define TESTCORE_H_



#include <string>



class Core

{

protected:

    static unsigned int id_seed;

    unsigned int id;

    std::string status;



public:

    friend class CPU;

    Core();

    ~Core();



    virtual void procesare(std::string aplicatie) = 0;

};





class CoreScreen: public Core

{

public:

    CoreScreen();

    ~CoreScreen();



    void procesare(std::string aplicatie);

};

#endif /* TESTCORE_H_ */

TestCore.cpp:

/*

 * TestCore.cpp

 */

#include <iostream>

#include <fstream>

#include "TestCore.h"



Core::Core()

{

    std::cout << "Core::Core()..." << std::endl;

}



Core::~Core()

{

    std::cout << "Core::~Core()..." << std::endl;

}



CoreScreen::CoreScreen()

{

    std::cout << "CoreScreen::CoreScreen()..." << std::endl;

}



CoreScreen::~CoreScreen()

{

    std::cout << "CoreScreen::~CoreScreen()..." << std::endl;

}



void CoreScreen::procesare(std::string aplicatie)

{

    std::cout << "CoreScreen::procesare(" << aplicatie << ")"  << std::endl;;

}



int main () {

    std::cout << ">>main()..." << std::endl;

    CoreScreen CS1, CS2, CS3, CS4;

    CS1.procesare("Testing CS1");

    std::cout << "<<main()." << std::endl;

    return 0;

}

SAMPLE OUTPUT:

>>main()...

Core::Core()...

CoreScreen::CoreScreen()...

Core::Core()...

CoreScreen::CoreScreen()...

Core::Core()...

CoreScreen::CoreScreen()...

Core::Core()...

CoreScreen::CoreScreen()...

CoreScreen::procesare(Testing CS1)

<<main().

You'll note that I implemented Core::Core() and Core::~Core(). If you don't need them - then don't even put them in your .h class definition.

'Hope that helps