The Qt Framework is based on a C++ library, so the integration should be similar to other third party C++ libraries.
Qt Framework can deploy applications to a variety of platforms. For Windows, there is an option to build Qt as a shared library
<http://doc.trolltech.com/4.1/deployment-windows.html>
In terms of integrating to S-Functions, you can load these shared libraries and make function calls from the deployed Qt application.
Additionally, Simulink S-Functions have multiple entry points. This means that depending on the action being called in Simulink, it calls a certain portion of the code in S-Function.
Therefore, users should be aware of the S-Function structure when interfacing with Qt function calls.
However, please note that one cannot simply link against the Qt libraries that are already included in the MATLAB installation.
