change qDebug display level at runtime after program startup

James Mark Chan

Does anyone know if it is possible to change the display of statements of qDebug() duration execution as opposed to startup?

https://stackoverflow.com/questions/28540571/how-to-enable-and-disable-qdebug-messages

JonB

@James-Mark-Chan
As described in the link you reference, all qDebug() statements go via https://doc.qt.io/qt-5/qtglobal.html#qInstallMessageHandler, where you can do whatever you like at runtime with appropriate code. What is it that you cannot achieve that way?

James Mark Chan

Looks like calling qInstallMessageHandler(myMessageOutput); replaces the default message handler which I believe will work for us. I though it added a message handler in addition to the default one and the default one could be configured further in some way.

JonB

@James-Mark-Chan
You can indeed only have one message handler. Calling qInstallMessageHandler() replaces any current one. The docs state:

Only one message handler can be defined, since this is usually done on an application-wide basis to control debug output.

However, because the method returns a QtMessageHandler

Installs a Qt message handler which has been defined previously. Returns a pointer to the previous message handler.

[My bold.] That means if you had a current/previous one which you still wanted under whatever circumstances, save this returned pointer and use it from your newly-installed one to call the original code in addition/instead of/as appropriate.