Hi, In my Qt5 project i have multiple classes, inside each class they are a few qDebug() << message; is it possible to enable/disable this qDebug() lines in a particular classe ? exemple of what i want to do : class A: public QObject { Q_OBJECT public: A(); ~A(){} Q_INVOKABLE void connecToServer(){ conn->start(); if(dbg){ qDebug()<<"started !" } } private: bool dbg = true; }; Is there a way to do this without de 'if' statement ? Thx in advance LA

Hi @LeLev, you might also be interested in Qt's categorized logging function: http://blog.qt.io/blog/2014/03/11/qt-weekly-1-categorized-logging/ With that, you can enable/disable logging at runtime . You just need to replace qDebug by qCDebug and add appropriate categories. Regards.

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How to enable and disable qDebug() messages inside a class

Solved General and Desktop

21 Posts 5 Posters 11.6k Views

J JonB
8 Jun 2022, 10:29
@QtTester
Now you are getting demanding!

The effect of #if !defined(QT_NO_DEBUG_OUTPUT) is acted on in qloggingcategory.h (https://code.woboq.org/qt5/qtbase/src/corelib/io/qloggingcategory.h.html#121).

Since that, like all Qt header files, is inside a #ifndef QLOGGINGCATEGORY_H guard, that file is only read/included the first time that file is included into any particular source file. So switching QT_NO_DEBUG_OUTPUT on & off within one file won't have the effect you seem to want.

You could presumably achieve the same effect to "scope" the enablement/disablement with something based on:
```
// Next line at *beginning* of your header file
#undef qCDebug
#  define qCDebug(category, ...) QT_NO_QDEBUG_MACRO()

...

// Next line at *end* of your header file
#undef qCDebug
#  define qCDebug(category, ...) \
    for (bool qt_category_enabled = category().isDebugEnabled(); qt_category_enabled; qt_category_enabled = false) \
        QMessageLogger(QT_MESSAGELOG_FILE, QT_MESSAGELOG_LINE, QT_MESSAGELOG_FUNC, category().categoryName()).debug(__VA_ARGS__)
```
but it's getting messy, and relies on knowing what the definition of qCDebug is in Qt, which could change.

Better would be to write something other than qDebug() for whichever things you want to enable/disable, or use a dedicated category you define for those lines.
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wrote on 8 Jun 2022, 11:56 last edited by

#21

@JonB
we discuss and you give solution, others will be benefited, tripartite win. :-)
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8 Jun 2022, 11:56