How to print variables with qDebug?

[ricardo]

Hi friends!

Usually I use qDebug to print variables values, but I guess it must be an easy way. I use 2 lines, QString and toAscii method. Is there any shorter way to do this?

QString m=QString("x %1, y %2, w %3, h %4 ").arg(selection_center_x).arg(selection_center_y) .arg(selection_width).arg(selection_height);
qDebug(m.toAscii());

Thanks.

[rexi]

After including the QtDebug header, you can do something like

qDebug() << "x" << selection_center_x << "y" << selection_center_y << "w" << selection_width << "h" << selection_height;

qDebug() << "x" << selection_center_x << "y" << selection_center_y << "w" << selection_width << "h" << selection_height;

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[gsmiko]

Hi!

Try the stream operators! It's definitely shorter, but the code in the multi line approach is more manageable, it's easier to make small changes, or to reorganize the way variables are printed.

qDebug() << "x" << selection_center_x << ",y" << selection_center_y << ",w" << selection_width << ",h" << selection_height;

qDebug() << "x" << selection_center_x << ",y" << selection_center_y << ",w" << selection_width << ",h" << selection_height;

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Edit: Oops! Sorry rexi! It looks like you finished writing your post before me.

[ricardo]

Thanks.

I tried that but it does not work. Should I include any header?

1>.\CUtil.cpp(60) : error C2678: binary '<<' : no operator found which takes a left-hand operand of type 'QDebug' (or there is no acceptable conversion)
1>        c:\qt\2009.02\qt\include\qtcore\../../src/corelib/tools/qchar.h(389): could be 'QDataStream &operator <<(QDataStream &,const QChar &)'
1>        c:\qt\2009.02\qt\include\qtcore\../../src/corelib/tools/qbytearray.h(569): or 'QDataStream &operator <<(QDataStream &,const QByteArray &)'
1>        c:\qt\2009.02\qt\include\qtcore\../../src/corelib/tools/qstring.h(1062): or 'QDataStream &operator <<(QDataStream &,const QString &)'
1>        c:\qt\2009.02\qt\include\qtcore\../../src/corelib/kernel/qobject.h(471): or 'QDebug operator <<(QDebug,const QObject *)'
1>        c:\qt\2009.02\qt\include\qtcore\../../src/corelib/kernel/qcoreapplication.h(272): or 'QDebug operator <<(QDebug,const MSG &)'
1>        c:\qt\2009.02\qt\include\qtcore\../../src/corelib/tools/qpoint.h(103): or 'QDataStream &operator <<(QDataStream &,const QPoint &)'
1>        c:\qt\2009.02\qt\include\qtcore\../../src/corelib/tools/qpoint.h(181): or 'QDebug operator <<(QDebug,const QPoint &)'
1>        c:\qt\2009.02\qt\include\qtcore\../../src/corelib/tools/qpoint.h(235): or 'QDataStream &operator <<(QDataStream &,const QPointF &)'
1>        c:\qt\2009.02\qt\include\qtcore\../../src/corelib/tools/qpoint.h(354): or 'QDebug operator <<(QDebug,const QPointF &)'
1>        c:\qt\2009.02\qt\include\qtcore\../../src/corelib/tools/qsize.h(101): or 'QDataStream &operator <<(QDataStream &,const QSize &)'
1>        c:\qt\2009.02\qt\include\qtcore\../../src/corelib/tools/qsize.h(196): or 'QDebug operator <<(QDebug,const QSize &)'
1>        c:\qt\2009.02\qt\include\qtcore\../../src/corelib/tools/qsize.h(252): or 'QDataStream &operator <<(QDataStream &,const QSizeF &)'
1>        c:\qt\2009.02\qt\include\qtcore\../../src/corelib/tools/qsize.h(357): or 'QDebug operator <<(QDebug,const QSizeF &)'
1>        c:\qt\2009.02\qt\include\qtgui\../../src/gui/kernel/qcursor.h(151): or 'QDataStream &operator <<(QDataStream &,const QCursor &)'

1>.\CUtil.cpp(60) : error C2678: binary '<<' : no operator found which takes a left-hand operand of type 'QDebug' (or there is no acceptable conversion)
1>        c:\qt\2009.02\qt\include\qtcore\../../src/corelib/tools/qchar.h(389): could be 'QDataStream &operator <<(QDataStream &,const QChar &)'
1>        c:\qt\2009.02\qt\include\qtcore\../../src/corelib/tools/qbytearray.h(569): or 'QDataStream &operator <<(QDataStream &,const QByteArray &)'
1>        c:\qt\2009.02\qt\include\qtcore\../../src/corelib/tools/qstring.h(1062): or 'QDataStream &operator <<(QDataStream &,const QString &)'
1>        c:\qt\2009.02\qt\include\qtcore\../../src/corelib/kernel/qobject.h(471): or 'QDebug operator <<(QDebug,const QObject *)'
1>        c:\qt\2009.02\qt\include\qtcore\../../src/corelib/kernel/qcoreapplication.h(272): or 'QDebug operator <<(QDebug,const MSG &)'
1>        c:\qt\2009.02\qt\include\qtcore\../../src/corelib/tools/qpoint.h(103): or 'QDataStream &operator <<(QDataStream &,const QPoint &)'
1>        c:\qt\2009.02\qt\include\qtcore\../../src/corelib/tools/qpoint.h(181): or 'QDebug operator <<(QDebug,const QPoint &)'
1>        c:\qt\2009.02\qt\include\qtcore\../../src/corelib/tools/qpoint.h(235): or 'QDataStream &operator <<(QDataStream &,const QPointF &)'
1>        c:\qt\2009.02\qt\include\qtcore\../../src/corelib/tools/qpoint.h(354): or 'QDebug operator <<(QDebug,const QPointF &)'
1>        c:\qt\2009.02\qt\include\qtcore\../../src/corelib/tools/qsize.h(101): or 'QDataStream &operator <<(QDataStream &,const QSize &)'
1>        c:\qt\2009.02\qt\include\qtcore\../../src/corelib/tools/qsize.h(196): or 'QDebug operator <<(QDebug,const QSize &)'
1>        c:\qt\2009.02\qt\include\qtcore\../../src/corelib/tools/qsize.h(252): or 'QDataStream &operator <<(QDataStream &,const QSizeF &)'
1>        c:\qt\2009.02\qt\include\qtcore\../../src/corelib/tools/qsize.h(357): or 'QDebug operator <<(QDebug,const QSizeF &)'
1>        c:\qt\2009.02\qt\include\qtgui\../../src/gui/kernel/qcursor.h(151): or 'QDataStream &operator <<(QDataStream &,const QCursor &)'

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[gsmiko]

#include <QDebug> should be enough.

[drhex]

qDebug("x %d, y %d, w %d, h %d", selection_center_x, selection_center_y, selection_width, selection_height);

qDebug("x %d, y %d, w %d, h %d", selection_center_x, selection_center_y, selection_width, selection_height);

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should work with no extra headers

[ricardo]

No idea what is going on, but if I add #include <QDebug> it works. If I remove it, it odes not work. However qDebug("dsadsads"); works without #include <QDebug>.

Thanks.

[wysota]

If you're wondering why it happens, take a look at contents of the QtDebug header file (or rather the file it includes).