Question

I have Packet class contains virtual method and I have LogInRequest class which extends the packet class

Packet.h file

class Packet {

public:
    Packet();
    virtual ~Packet();

protected:
    virtual char* toByte() = 0;
    virtual void fromByte(char *d) = 0;
    virtual Packet* handle() = 0;

    short m_bodySize;
    int64_t m_deviceId;
};


/*
 * LogInRequestPacket
 */
class LogInRequestPacket: public Packet{

public:

    LogInRequestPacket();
    virtual ~LogInRequestPacket();

    virtual char* toByte();
    virtual void fromByte(char *d);
    virtual Packet* handle();
};

Packet.cpp file

#include "Packet.h"

Packet::Packet() {
    // TODO Auto-generated constructor stub

}

Packet::~Packet() {
    // TODO Auto-generated destructor stub
}

/*
 * LogInRequestPacket
 */
LogInRequestPacket::LogInRequestPacket(){
    printf("LogInRequestPacket is being created... \n");
}

LogInRequestPacket::~LogInRequestPacket(){

}

char* LogInRequestPacket::toByte(){

}

void LogInRequestPacket::fromByte(char *d){

}

Packet* LogInRequestPacket::handle(){

}

I am trying to create this LogInRequestPacket from factory like this

Packet *packet = m_packetFactory->createInstance(static_cast<PACKET_TYPES>(type));
packet->fromByte(pdata);

And it seems like trying to call the protected virtual fromByte function instead of the child class’s fromByte function.

I am getting a red line at the line declaring “virtual void fromByte(char *d) = 0” in Packet class scope in Packet.h file and it complains “… is protected”

Also, it complains too with x within context

packet->fromByte(pdata);

How do I fix this problem. Thanks in advance…

Answer 1

When you try to call a method through a pointer or reference, the compiler will verify the access specifier of the function in the static type of the object, even if it will dispatch the call to the dynamic type.

In your Packet class you have stated that you don’t want user code (other than Packet, friends and derived classes) to be able to call the methods, and the compiler is just telling you that. If those functions should be accessible from other code, make them public:

class Packet {
public:
    Packet();
    virtual ~Packet();

    virtual char* toByte() = 0;
    virtual void fromByte(char *d) = 0;
    virtual Packet* handle() = 0;
protected:
    short m_bodySize;
    int64_t m_deviceId;
};