Qt 5.2.0 and Qwt 6.1.0

Hi

I will show you the error and my project files.

Error:

Quote:

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Starting D:\Documents\Qt\QwtExamples\0003_EmptyPlot_for_Qt5 \build-EmptyPlot_for_Qt5-Desktop_Qt_5_2_0_MinGW_32bit-Debug\debug\EmptyPlot_for_Qt5.exe...
QWidget: Must construct a QApplication before a QWidget
Invalid parameter passed to C runtime function.
Invalid parameter passed to C runtime function.

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EmptyPlot_for_Qt5.pro

Code:

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QWT_LOCATION = c:/Qwt-6.1.0
INCLUDEPATH += $${QWT_LOCATION}/include
LIBS = -L$${QWT_LOCATION}/lib \
     -lqwt
 
greaterThan(QT_MAJOR_VERSION, 4): QT += widgets
 
SOURCES += \
    main.cpp

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main.cpp

Code:

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#include <QApplication>
#include <qwt_plot.h>
 
int main(int argc, char **argv)
{
    QApplication app(argc, argv);
 
    QwtPlot plot;
    plot.show();
 
    return app.exec();
}

---

Thank you!

AFAIR this is a build issue unrelated to fhe Qt or Qwt version. Look into the archive how to solve it ( I don't use Windows myself but it might be because of "DEFINES *= QWT_DLL" is missing ).

To avoid issues like this one install Qwt in the recommended way and use "CONFIG += qwt" instead of ttrying to figure out your profile manually. But if you insist on doing it yourself - at least have a look at qwt.prf to see what needs to be done.

Uwe

Quote:

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I don't use Windows myself but it might be because of "DEFINES *= QWT_DLL" is missing

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Where? I don't understand. Before installing? What is the file?

Quote:

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To avoid issues like this one install Qwt in the recommended way and use "CONFIG += qwt"

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What is "recommended way"? I installed qwt like this:

- in "qwtbuild.pri":

Quote:

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#CONFIG += silent

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- in console:

Quote:

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qmake qwt.pro
mingw32-make
mingw32-make install

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- I see this files in "C:\Qwt-6.1.0\lib":

Quote:

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libqwt.a
libqwtd.a
qwt.dll
qwt.lib
qwtd.dll
qwtd.lib

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I just had the same problem. Try linking to "-lqwtd" instead if you are going to use debugging.