Enable debugging
To specify settings for running applications on the Run device that you select for a kit, go to Projects > Run Settings.

To select the languages to debug, select a combination of them in Debugger Settings > Debug. Select Automatic to derive the languages from the contents of the project.
C++ and QML (combined engine, experimental) debugs both languages in a single engine. Only some debuggers support it, and it needs Qt Creator to launch the application, so it is not available for Android, iOS, Boot2Qt, or Qt Application Manager.
Debug C++
In Additional startup commands, you can enter additional settings for debugging C++:
- Custom debugging helpers
- GDB commands to execute after GDB has started, but before the debugged program is started or attached, and before the debugging helpers are initialized
However, you can usually leave this field empty.
Debug Qt Quick
Opening a socket at a well-known port presents a security risk. Anyone on the Internet could connect to the application that you are debugging and execute any JavaScript functions. Therefore, make sure that the port is properly protected by a firewall.
To create a build configuration that supports debugging for a Qt Quick application project, you also need to enable QML debugging either globally or in the Build Settings of the project.
See also Building and running projects, How To: Debug, Debugging, and Debuggers.