A question that pops up every now and again and this time I'll document my attempt to do this. To do this I use the Qt framework. More specifically, I used QtcpSocket for the connection.

In this example program I will use a client-server approach to this problem. I will build a server that accepts one or more connections and can receive images. I will also build a client that can connect to the server and send an image.

The Client-Server architecture

Most of the code that set up the actuall connection have been borrowed from the  program. In this example a client-server system is build. What I removed from this example is all the GUI interfacing and the functions that receive and send the messages. The first is because I do not need a GUI here as I will use it as a lib, and the latter is because I do not need to send and receive QString objects (and more important, I do not have to forward them to all other connected clients).

So If you want a deeper understanding of how the connection is set-up and how the server deals with multiple connections, then I point forward to the  at .

How to send an image

Here I will actually cover how to send an image. In Qt this is rather easy. For the sake of structure, I will first describe the client-side process and then the server-side process.

Sending the image (Client-side process)

What I need to do is to convert the image to a byte-array and then send this byte-array over the network. As we are using the Qt framework, I assume that the image is already a QImage object and the socket has been set-up by following the Simple chat example. Then sending the image is rather easy:// To load a QImage//QImage image;        // See the documentation on how to use QImage objects//image.load("test.png", "PNG");// To set-up the socket//socket->connectToHost(address, port, QIODevice::WriteOnly)QByteArray ba;              // Construct a QByteArray objectQBuffer buffer(&ba);        // Construct a QBuffer object using the QbyteArrayimage.save(&buffer, "PNG"); // Save the QImage data into the QBuffersocket->write(ba);          // Send the QBuffer (QbyteArray) over a socket

And that is it! Yes, there are some beautifications possible, but this is the trick!

Receiving the image (Server-side process)

Here I need to convert the incoming stream back into an image. This is basically as easy as sending it, but I will anyway show it. Also here I assume that there is a listening socket available, but I also assume that the buffer. This time no example code on that, as it takes more lines to describe.

// Available are://QTcpSocket* socket;//QBuffer* buffer = buffers.value(socket);qint64 bytes = buffer->write(socket->readAll()); // Read all the received bytesbuffer->seek(buffer->pos() - bytes);  // go back as many bytes as we just wrote so that it can be readQImage image;			      // Construct a new QImageimage.loadFromData(buffer->buffer()); // Load the image from the receive bufferif (image.isNull())		      // Check if the image was indeed received        qDebug("The image is null. Something failed.");// If it did not fail, the image is now in the QImage object again

It could hardly be simpler, isn't it?

Extra: Send the image name as well

If you want the client-side to give a name to this image then this is perfectly possible by using some interesting options from the QImage object. To attach the image name as a tag to the image use:

//QImage image has already  been constructedimage.setText("name", name);

On the receiving end we can retrieve this tag information easily using:

//QImage image has already  been constructedimage.text("name")

This leaves us with a lot of interesting possibilities... so be sure you check those out as well!

Final notes

Well, I took also the liberty to put this in code so you can download it, test it, and learn from it. You can find the source code .

If you have any comments or questions on the code then leave a comment below or send me an e-mail. If you make some changes in the code then I am happy to receive those changes as well (as diff or as new zip file).

I hope this was helpful for you!