C++ How can I send an object via socket?

Question

I have a question for you.

I have this class:

`

#define DIMBLOCK 128
#ifndef _BLOCCO_
#define _BLOCCO_

class blocco
{
    public:
        int ID;
        char* data;


        blocco(int id);
};

#endif




blocco::blocco(int id)
{
    ID = id;
    data = new char[DIMBLOCK];
}

`

and the application has a client and a server. In the main of my server I instantiate an object of this class in this way: blocco a(1);

After that I open a connection between the client and the server using sockets. The question is: how can I send this object from the server to the client or viceversa? Could you help me please?

Answer 1

It's impossible to send objects across a TCP connection in the literal sense. Sockets only know how to transmit and receive a stream of bytes. So what you can do is send a series of bytes across the TCP connection, formatted in such a way that the receiving program knows how to interpret them and create an object that is identical to the one the sending program wanted to send.

That process is called serialization (and deserialization on the receiving side). Serialization isn't built in to the C++ language itself, so you'll need some code to do it. It can be done by hand, or using XML, or via Google's Protocol Buffers, or by converting the object to human-readable-text and sending the text, or any of a number of other ways.

Have a look here for more info.

Answer 2

you can do this using serialization. This means pulling object into pieces so you can send these elements over the socket. Then you need to reconstruct your class in the other end of connection. in Qt there is QDataStream class available providing such functionality. In combination with a QByteArray you can create a data package which you can send. Idea is simple:

Sender:

QByteArray buffer;
QDataStream out(&buffer);
out << someData << someMoreData;

Receiver:

QByteArray buffer;
QDataStream in(&buffer);
in >> someData >> someMoreData;

Now you might want to provide additional constructor:

class blocco
{
    public:
        blocco(QDataStream& in){
            // construct from QDataStream
        }

        //or
        blocco(int id, char* data){
            //from data
        }
        int ID;
        char* data;


        blocco(int id);
};

extended example

Answer 3

I don't know how much flak I'll get for this, but well I tried this and though I should share it. I am a beginner at socket programming so don't get pissed off.

What I did is I created an array of characters which is of the size of the class (representing the block of memory at the server side). Then I recved the block of memory at the client side and typecast that block of memory as an object and voila!! I managed to send an object from client to server.

Sample code:

blocco *data;
char blockOfData[sizeof(*data)];

if(recv(serverSocket, blockOfData, sizeof(*data), 0) == -1) {
    cerr << "Error while receiving!!" << endl;
    return 1;
}

data = (blocco *)blockOfData;

Now you can do whatever you want with this data using this as a pointer to the object. Just remember do not try to delete/free this pointer as this memory is assigned to the array blockOfData which is on the stack.

Hope this helps if you wanted to implement something like this.

PS: If you think what I've done is poor way of coding please let me know why. I don't know why this is such a bad idea(if it is in fact a bad idea to do this). Thanks!!