Why does this defined QT_NO_DEBUG_OUTPUT not supress the qDebug?

DragonautX

I was reading about the qDebug() function in the docs, and one sentence in the description said: "This function does nothing if QT_NO_DEBUG_OUTPUT was defined during compilation". I decided to try some test code in QtCreator with a #define QT_NO_DEBUG_OUTPUT and a qDebug(). I built the project and ran it, but the Application Output still showed my qDebug text. Why did my QT_NO_DEBUG_OUTPUT definition not keep qDebug from outputting to the Application Output, as the docs say it's used for?

#include <QtWidgets>
#define QT_NO_DEBUG_OUTPUT

int main(int argc, char *argv[]) {
    QApplication app(argc, argv);
    QWidget window;
    window.resize(320, 340);
    window.show();

    qDebug() << "This is a qDebug test";

    return app.exec();
}

mrjj

Hi
Did you make a release build ?
As far as i know, QT_NO_DEBUG_OUTPUT removes qDebug for release builds only.

DragonautX

Oh, I was doing a Debug build. I switched to release build, cleaned, ran qmake, did a build, and did Ctrl+R to run, but the qDebug message is still showing in QtCreator's Application Output. Do you know anything else I can try?

mrjj

@DragonautX
Ok that's odd.
I use
CONFIG(release, debug|release):DEFINES += QT_NO_DEBUG_OUTPUT

Let me check if it still works :)

DragonautX

Oh wait, it's my .pro file that's the problem. I added the line you said you used, cleaned, qmake, built, and ran, and it worked. I didn't know you were supposed to add that line to your .pro. I thought a #define would work just fine by itself?

QT += widgets

SOURCES += \
    main.cpp

CONFIG(release, debug|release):DEFINES += QT_NO_DEBUG_OUTPUT

mrjj

@DragonautX
seems fine. make sure to really clean build folder.

mrjj

@DragonautX
Just tested in this sample
https://www.dropbox.com/s/oaf75jo0awpm1fc/mydebug.zip?dl=0
Works here in Qt5.7 win 10.

DragonautX

Ya, it worked. I guess I was clicking too fast and forgot to really clean. It works for both the #define preprocessor and the .pro code. Anyways, thanks for the help and uploading an example too. That was helpful. I'll make sure to check next time if I'm Debug or Release mode.

mrjj

@DragonautX
Super
As last note:
I find this pretty nice

qDebug()<<__FILE__<<__LINE__<<__PRETTY_FUNCTION__;

DragonautX

That's pretty cool. Didn't know predefined macros like that were there before. wasn't able to use __PRETTY_FUNCTION__, but __FUNCTION__ worked. From SO, seems like __PRETTY_FUNCTION__ is only for some gcc compiler, and Qt says I'm using mvsc. Is it supposed to work with mvsc too? That's how all my test projects have been compiled on so far by Qt.

mrjj

@DragonautX said in Why does this defined QT_NO_DEBUG_OUTPUT not supress the qDebug?:

PRETTY_FUNCTION

oh yes, sorry, its gcc
I think Vs have

__FUNCDNAME__; // Decorated
__FUNCSIG__; // Signature
and 
__FUNCTION__; //should be same

Didnt test lately, but it does have something the same.

DragonautX

Alright, cool. Thanks for the tip!

SGaist

Hi,

Otherwise you can use Q_FUNC_INFO. Shorter to write :)