In Qt Creator on Windows, qDebug() statements don't work, and the following message appears in the output window:
Cannot retrieve debugging output.
How can it be fixed?
This problem can show up if more than one instance of Qt Creator is active. To fix the issue, simply close all the other instances of Qt Creator and it should work.
For me, I solved the problem by simply closing the running application built with the other qt creator. So not necessary to close the other qt creator.
Or you may be running a version of DebugView from Sysinternals, that causes the same result.
For me this error message appears when I have more than one instance of my application, not of Qt Creator.
来源：https://stackoverflow.com/questions/14379325/cannot-retrieve-debugging-output-in-qt-creator