I have a simple Win32 GUI app which has an edit control in the main window. If I write:
printf(\"Hello world!\\n\");
I would like the text
You can do that in Windows by redirecting stdout when you create the process. You do so by setting flags and setting some handles in the STARTUPINFO structure passed to CreateProcess. See this example on MSDN for detail on how to set this up.
Once you have that setup can use ReadFile to read from the redirected stdout of the console process then send it to the edit control.