Qwt 6.3.0 (from qwt-code-r2921-trunk) compilation fails on Ubuntu 18.04.

[kuzulis]

Hi.

I need to port the Qwt build system from the qmake to QBS in my project. Previous Qwt stable version 6.2.0 was compiled successfully on any Linux. But now I have updated it to the version from the trunk r2921.

And right now compilation fails with following errors:

/usr/bin/g++ -g -O0 -Wall -Wextra -m64 -pipe -fexceptions -fvisibility=hidden -fvisibility-inlines-hidden -fPIC -DQWT_MOC_INCLUDE=1 -DQWT_NO_SVG -DQT_CONCURRENT_LIB -DQT_CORE_LIB -DQT_GUI_LIB -DQT_OPENGL_LIB -DQT_WIDGETS_LIB -DQT_PRINTSUPPORT_LIB -DQT_SVG_LIB -I/home/denis/Documents/Projects/project-git/project/src/libs -I/opt/Qt/5.9.6/gcc_64/include -I/opt/Qt/5.9.6/gcc_64/include/QtConcurrent -I/opt/Qt/5.9.6/gcc_64/include/QtCore -I/opt/Qt/5.9.6/gcc_64/mkspecs/linux-g++ -I/home/denis/Documents/Projects/project-git/build-project-desktop-debug/qtc_Desktop_Qt_5_9_6_GCC_64bit_Debug/qwt.91a462ca/qt.headers -I/opt/Qt/5.9.6/gcc_64/include/QtGui -I/opt/Qt/5.9.6/gcc_64/include/QtOpenGL -I/opt/Qt/5.9.6/gcc_64/include/QtWidgets -I/opt/Qt/5.9.6/gcc_64/include/QtPrintSupport -I/opt/Qt/5.9.6/gcc_64/include/QtSvg -std=c++14 -o /home/denis/Documents/Projects/project-git/build-project-desktop-debug/qtc_Desktop_Qt_5_9_6_GCC_64bit_Debug/qwt.91a462ca/3a52ce780950d4d9/qwt_plot.cpp.o -c /home/denis/Documents/Projects/project-git/project/src/libs/qwt/qwt_plot.cpp
In file included from /opt/Qt/5.9.6/gcc_64/include/QtCore/qmetatype.h:49:0,
from /home/denis/Documents/Projects/project-git/project/src/libs/qwt/qwt_plot_item.h:14,
from /home/denis/Documents/Projects/project-git/project/src/libs/qwt/qwt_plot_dict.h:15,
from /home/denis/Documents/Projects/project-git/project/src/libs/qwt/qwt_plot.h:14,
from /home/denis/Documents/Projects/project-git/project/src/libs/qwt/qwt_plot.cpp:10:
/home/denis/Documents/Projects/project-git/project/src/libs/qwt/qwt_plot.cpp: In function ‘void qwtEnableLegendItems(QwtPlot*, bool)’:
/opt/Qt/5.9.6/gcc_64/include/QtCore/qobjectdefs.h:271:35: error: initializer fails to determine size of ‘sig’
# define SIGNAL(a) qFlagLocation("2"#a QLOCATION)
~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~
/home/denis/Documents/Projects/project-git/project/src/libs/qwt/qwt_plot.cpp:29:24: note: in expansion of macro ‘SIGNAL’
const char sig[] = SIGNAL(legendDataChanged(QVariant,QList<QwtLegendD ata>));
^~~~~~
/opt/Qt/5.9.6/gcc_64/include/QtCore/qobjectdefs.h:271:35: error: array must be initialized with a brace-enclosed initializer
# define SIGNAL(a) qFlagLocation("2"#a QLOCATION)
~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~
/home/denis/Documents/Projects/project-git/project/src/libs/qwt/qwt_plot.cpp:29:24: note: in expansion of macro ‘SIGNAL’
const char sig[] = SIGNAL(legendDataChanged(QVariant,QList<QwtLegendD ata>));
^~~~~~
/opt/Qt/5.9.6/gcc_64/include/QtCore/qobjectdefs.h:270:35: error: initializer fails to determine size of ‘slot’
# define SLOT(a) qFlagLocation("1"#a QLOCATION)
~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~
/home/denis/Documents/Projects/project-git/project/src/libs/qwt/qwt_plot.cpp:30:25: note: in expansion of macro ‘SLOT’
const char slot[] = SLOT(updateLegendItems(QVariant,QList<QwtLegendDat a>));
^~~~
/opt/Qt/5.9.6/gcc_64/include/QtCore/qobjectdefs.h:270:35: error: array must be initialized with a brace-enclosed initializer
# define SLOT(a) qFlagLocation("1"#a QLOCATION)
~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~
/home/denis/Documents/Projects/project-git/project/src/libs/qwt/qwt_plot.cpp:30:25: note: in expansion of macro ‘SLOT’
const char slot[] = SLOT(updateLegendItems(QVariant,QList<QwtLegendDat a>));
^~~~
Process failed with exit code 1.

My env is:

* Ubuntu 18.04 LTS 64 bit
* GCC 7.3.0
* Qt official 5.9.6

PS: Hovewer on Windows it compiles successfully with MSVC2015 32-bit && Qt 5.9.6.

[Uwe]

I compiled the file with your options on my box without problems, but on my box it is a gcc 7.3.1.

What happens, when changing the offending lines from:

const char sig[] = ...

const char sig[] = ...

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to

const char* sig = ...

const char* sig = ...

To copy to clipboard, switch view to plain text mode 

Or do you see another way to change the code to work around the compiler issue - bside writing the SIGNAL/SLOT signatures twice ?

Uwe

PS1: your compiler flags differ from those you find in qwtbuild.pri. At least -fno-math-errno -funsafe-math-optimizations should have an impact on the performance, when using methods from cmath. Also you should use a higher optimization level.
PS2: do you see an effect on your CPU usage, when enabling QwtPlotCurve::FilterPointsAggressive ?

[kuzulis]

> What happens, when changing the offending lines from:

Yes, many thanks, with:

const char* sig = ...

const char* sig = ...

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it is successfully compiled.

[Uwe]

Weird - seems to be a compiler bug of gcc 7.3.0.

I will adjust the code - thanks for reporting,

Uwe