can’t access my inherited class attributes

I am working on a project for my job to encode/decode into buffers DNS Records objects in C++. Some records have the same infos, so I created a class Dns message with theses basic infos:

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

    virtual int GetSize() = 0;
    uint32_t       m_ttl; 
    DnsClass       dclass; 
    DnsType        type; 
    std::string    m_domain;    
};

The DnsClass and DnsTypes are enum with the differents class/types I use. Then I have my sub-classes for each record, I will take A for the example:

class CDns_RR_A : public CDnsMessage
{
public:
    CDns_RR_A();

    virtual ~CDns_RR_A();
    virtual int GetSize(CDnsMessage const& msg);

    uint32_t        m_address;
};

Then I have my encode/decode function in another header, encoder.h and encoder.cpp.

I am receiving a DnsMessage (the object) and receiving buffer, and I encode or decode. So I used dynamic cast to know which type of record it is, and adapt the encode and decode to the variables the object has. here is my decode for example:

EncodeResult DecodeData(const char * buffer,CDnsMessage & msg,std::size_t size)
{
    EncodeResult res(ENCODE_OK);

    uint32 ttl = 0;
    eDnsClass dnsclass;
    eDnsType  dnstype;

    //decoding RR_A
    if(CDns_RR_A* RR_A_msg = dynamic_cast< CDns_RR_A* >( &msg ))
    {       
        uint32_t address;

        dnsclass = CLASS_IN;
        msg.dclass = dnsclass;
        dnstype = TYPE_A;
        msg.type = dnstype;

        res = DecodeInt32(&buffer,&size,&ttl);
        CHECK_DECODE_ERROR(res);
        msg.m_ttl = ttl;

        res = DecodeInt32(&buffer,&size,&address);
        CHECK_DECODE_ERROR(res);
        msg.m_address = address;
    }
}

The DecodeInt32 is a function made by people before long time ago, it takes a buffer (char**), a size_t* and a uint32.

I have two problems, first I can’t access the members of my subclass, when I compile I got a problem with msg.dclass or msg.type and It says “request for member ‘class’ in ‘RR_A_msg’, which is of non-class type ‘CDns_RR_A*’ but I don’t understand, if my dynamic cast works it mean that the msg received waiting to be fulfilled is of type A no?

And my second problem is: I am using uint32_t for the ttl (imposed by enterprise) and my decodeint32 takes uint32 so the compiler says invalid conversion from uint32_t* to uint32.

Is there away to convert one to another?

Edit: Updated my code following answers and advices, now i have

if(dynamic_cast< CDns_RR_A* >( &msg ) != nullptr)
                            {       
                                    CDns_RR_A* RR_A_msg = dynamic_cast< CDns_RR_A* >( &msg )

                                    uint32 address;

                                    dnsclass = CLASS_IN;
                                    RR_A_msg->dclass = dnsclass;
                                    dnstype = TYPE_A;
                                    RR_A_msg->type = dnstype;

                                    res = DecodeInt32(&buffer,&size,&ttl);
                                    CHECK_DECODE_ERROR(res);
                                    RR_A_msg->m_ttl = ttl;

                                    res = DecodeInt32(&buffer,&size,&address);
                                    CHECK_DECODE_ERROR(res);
                                    RR_A_msg->m_address = address;
                            }

Changing uint32_t to uint32 for decode worked, and having RR_A_msg-> instead of msg. worked too. But now i have undefined reference totypeinfo for CDns_RR_A’`

Answer

For the “you cannot convert uint32_t* to uint32” the issue is that the former is a pointer and the later is not. You should take the & off the front and pass the value not a pointer to it.

I don’t know why you can’t get the class member (maybe related to using a reserved name as a variable?) but you shouldn’t be able to access m_address in this way.

Instead of

msg.m_address

You need to be using

RR_A_msg->m_address

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Answer