Plain old console output is still a valuable debugging tool, even when used in a GUI application.
There are many tools here in CP that can be combined with console output like:
CConsole - a simple console for debug output
Creating a console for your MFC app's debug output
You can use printf, sprintf or any similar to build the output strings.
Computer Electronics professional, Software Architect and senior Windows C++ and C# developer with experience in many other programming languages, platforms and application areas including communications, simulation systems, PACS/DICOM (radiology), GIS, 3D graphics and HTML5-based web applications.
Currently intensively working with Visual C# 2013 and TFS.