Disable qDebug output locally with a macro

Question

I used qDebug all over the code. Now I would like to limit its output by translation units, defining a separate macro to enable/disable qDebug output in a translation unit:

test.pro:

DEFINES += NO_DEBUG_ONE

testone.cpp:

#ifdef NO_DEBUG_ONE
#define QT_NO_DEBUG_OUTPUT
#endif

testtwo.cpp:

#ifdef NO_DEBUG_TWO
#define QT_NO_DEBUG_OUTPUT
#endif

So, setting macros like this I expected to get qDebug output only in testtwo.cpp, but I see the qDebug messages from both translation units.

What am I missing here and how to solve it?

Are you setting those defines before including *any* Qt header? — peppe, Oct 19 '15 at 07:12

score 3 · Accepted Answer · answered Oct 19 '15 at 07:49

3

Move your code to the top of testone.cpp and testtwo.cpp and you should be good to go.

You can use QT_NO_DEBUG_OUTPUT and QT_NO_WARNING_OUTPUT when you compile your app but those must be set before the Qt headers are included.

Using cmake you could add those defines on a per-file base but I don't see a simple way doing that with qmake.

answered Oct 19 '15 at 07:49

Simon Warta

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Thank you, I finally found time to test it and it works as expected! – rightaway717 Mar 23 '16 at 07:59

Gabrielle de Grimouard · Answer 2 · 2015-10-17T09:05:23.450

0

As it's a QMake macro I don't think you can do it locally. the only way is to use a standard macro as -D TEST and after do thing like that.

#ifndef TEST
    qDebug() << "test";
#endif

edited Oct 17 '15 at 09:05

answered Oct 17 '15 at 08:51

Gabrielle de Grimouard

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I tried just now, but no difference. It passes this macro to preprocessor just the way DEFINES do. I see it in compilation output. though thanx for try – rightaway717 Oct 17 '15 at 08:56
or else you can just do #ifndef TEST qDebug() << "test"; #endif for each qdebug you want to remove with your macro – Gabrielle de Grimouard Oct 17 '15 at 08:58
that is not an option. I have to spend hours or days of work to change that. – rightaway717 Oct 17 '15 at 09:05
as it's a qmake macro I don't think you can do it. this macro will be use to change the makefile not each file I think – Gabrielle de Grimouard Oct 17 '15 at 09:06

score 0 · Answer 3 · edited Oct 19 '15 at 07:49

As Gabriel de Grimouard pointed out, the QT_NO_DEBUG_OUTPUT takes affect when you compile Qt, not your application (as far as I understand).

The only option is to change your code, there are a few options:

Do as suggested in his answer, make use of a Macro check before each debug

Define your own debug macro that you can enable or disable:

// Top of testone.cpp
#ifdef NO_DEBUG_ONE
  #define DEBUG_MESSAGE(message) 
#else
  #define DEBUG_MESSAGE(message) qDebug() << message
#endif
// In your code
DEBUG_MESSAGE("This is my debug message");

The benefit of this is that you do not have #ifndef TEST everywhere in your code.

Make use of the Logging Categories in Qt (recommended)
- http://blog.qt.io/blog/2014/03/11/qt-weekly-1-categorized-logging/
- https://www.youtube.com/watch?v=GDtrbIs6JA0

Unfortunately all of these will require code changes.

Thank you for your answer, but please see Simon answer. It is possible — rightaway717, Mar 23 '16 at 08:01

Disable qDebug output locally with a macro

3 Answers3