Problem with TCP server/client (corrupted data)

[chris15001900]

Hi,
I'm developing a tcp-based server/client. I found a code to post a struct through tcp, but the data I get is looking weird. Here is what I have right now:

struct abc {
    char a;
    char b;
};
 
abc *a = (abc*)malloc(sizeof(struct abc));
a->a='1';
a->b = '2';
 
 QByteArray block;
 QDataStream out(&block, QIODevice::WriteOnly);
 out.setVersion(QDataStream::Qt_4_0);
 
         out << (void*)a;
 
          socket->write(block.data());

struct abc {
    char a;
    char b;
};

abc *a = (abc*)malloc(sizeof(struct abc));
a->a='1';
a->b = '2';

 QByteArray block;
 QDataStream out(&block, QIODevice::WriteOnly);
 out.setVersion(QDataStream::Qt_4_0);

         out << (void*)a;

          socket->write(block.data());

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And here is the code to receive it:

char *data = (char*)this->socket->readAll().data();
 
QDataStream in(data);
in.setVersion(QDataStream::Qt_4_0);
 
     QByteArray block;
     in >> block;
 
     abc *received;
     received = (abc*)data;

char *data = (char*)this->socket->readAll().data();

QDataStream in(data);
in.setVersion(QDataStream::Qt_4_0);

     QByteArray block;
     in >> block;
     
     abc *received;
     received = (abc*)data;

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And when I debug this data, there are many strange characters instead of chars... What can be wrong?

[wysota]

You are sending a pointer, that's probably not what you want since the pointer will point to a random location after it is received.

[chris15001900]

Thanks for the reply,
if I don't want a pointer, I can only send it through a reference, and the problem is the same (garbage data):

abc a;
a.a = '1';
a.b = '2';
 
out << &a;
 
socket->write(block.data());

abc a;
a.a = '1';
a.b = '2';

out << &a;

socket->write(block.data());

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Is there a way not to use a reference?

[wysota]

That's not the point. Using "&a" you are still sending a pointer (and not a reference). You need to send the data, for instance:

struct abc {
  char a;
  char b;
};
 
QDataStream& operator<<(QDataStream& stream, const abc &object) {
  stream << object.a << object.b;
  return stream;
}
 
 
QDataStream& operator>>(QDataStream& stream, abc &object) {
  stream >> object.a >> object.b;
  return stream;
}

struct abc {
  char a;
  char b;
};

QDataStream& operator<<(QDataStream& stream, const abc &object) {
  stream << object.a << object.b;
  return stream;
}


QDataStream& operator>>(QDataStream& stream, abc &object) {
  stream >> object.a >> object.b;
  return stream;
}

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and then you can do:

abc a;
a.a = '1';
a.b = '2';
QByteArray data;
QDataStream str(&data);
str << a;
socket->write(data); // btw. such code is practically useless, 
                     // the receiver doesn't know how much data to expect

abc a;
a.a = '1';
a.b = '2';
QByteArray data;
QDataStream str(&data);
str << a;
socket->write(data); // btw. such code is practically useless, 
                     // the receiver doesn't know how much data to expect

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Being lazy and trying to dump a memory block directly into the data stream is usually a bad idea.

[chris15001900]

Finally, I got the answer:

struct abc {
char a;
char b;
};
 
abc *ab;
ab = new abc;
 
 socket->write((char*)ab, sizeof(struct abc));

struct abc {
char a;
char b;
};

abc *ab;
ab = new abc;

 socket->write((char*)ab, sizeof(struct abc));

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Works perfect!

Oh, and I receive data like this:

abc *received;
 
QByteArray data = socket->readAll();
 
 received = (abc*)data.data();

abc *received;

QByteArray data = socket->readAll();

 received = (abc*)data.data();

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[wysota]

You are aware that your solution is not portable, right? Probably even between 32 and 64b platforms.