Qwt graph page crashes GUI

[koahnig]

@MShields

Just saw that you posted the same question again and one of the moderators closed it.

Did you contact Qwt's mailing list?
When you can limited your problem to Qwt it is really the best source to post there. However, in my opinion you shall make sure that it is not a general Qt problem then.

Also you shave a bit of an exotic issue. Therefore, out of personal experience you might have to wait longer than a day.

[A Former User]

While playing with the code I discovered that if i comment out the lines:

grid->setMajorPen(Qt::gray,1,Qt::Dashline);
grid->setMinorPen(Qt::gray,1,Qt::Dashline);
curve1->setPen(colour1);
curve1->setSymbol(symbol1)

grid is a QwtPlotGrid and curve1 is a QwtPlotCurve.

Then the code works. However i still need to change how the curve looks.

[koahnig]

The style of QwtPlotCurve can be changed with setStyle and setSymbol

[A Former User]

As noted setSymbol causes the program to crash

[koahnig]

@MShields said:

As noted setSymbol causes the program to crash

No, you didn't.

What is the symbol you are setting?

[A Former User]

@MShields said:

curve1->setSymbol(symbol1)

As shown in previous post, the last of the four commented out lines

[A Former User]

Full code is

QwtSymbol *symbola1 = new QwtSymbol( QwtSymbol::Ellipse, QBrush( Qt::black ), QPen( Qt::red, 2 ), QSize( 8, 8 ) );
curve1->setSymbol( symbola1 );

[koahnig]

So if you leave the other three lines and comment only the fourth line, the program is not crashing?

[A Former User]

To be clear it will crash when all four of these lines are commented out. The program will crash if any one of the four are uncommented.

[A Former User]

Here is the all the lines as is:

// grid->setMajorPen(Qt::gray, 1, Qt::DashLine);
// grid->setMinorPen(Qt::gray, 1, Qt::DashLine);

QColor colour1 = Qt::red;
// curve1->setPen(colour1);
QwtSymbol *symbola1 = new QwtSymbol( QwtSymbol::Ellipse, QBrush( Qt::black ), QPen( Qt::red, 2 ), QSize( 8, 8 ) );
// curve1->setSymbol( symbola1 );

If any of the lines which are commented out are uncommented out the the program crashs when it reachs that page.

[koahnig]

Is anywhere in the same scope "grid" or "curve1" used successfully?

[A Former User]

grid and curve1 are successfully used in other situations

e.g
grid->enableX(true);
grid->attach(myPlot);

curve1->setSamples(Column1, Column2, 26);
curve1->setYAxis(QwtPlot::yLeft);

[koahnig]

@MShields said:

grid and curve1 are successfully used in other situations

e.g
grid->enableX(true);
grid->attach(myPlot);

curve1->setSamples(Column1, Column2, 26);
curve1->setYAxis(QwtPlot::yLeft);

That might be, but the question is if they are still valid when you are trying to access where you the crash. E.g. try to modify curve1 with setSymbol when you are able to use those pointers successfully.

For instance this way:

curve1->setSamples(Column1, Column2, 26);
curve1->setYAxis(QwtPlot::yLeft);
QColor colour1 = Qt::red;
curve1->setPen(colour1);
QwtSymbol *symbola1 = new QwtSymbol( QwtSymbol::Ellipse, QBrush( Qt::black ), QPen( Qt::red, 2 ), QSize( 8, 8 ) );
curve1->setSymbol( symbola1 );

[A Former User]

That is how it is suppose to work, curve1 has setSamples, setYAxis, etc set up.
The problem is when setPen or setSymbol are added in. I have had to comment them out to prevent the program from crashing.

[koahnig]

I can come back only to the initial recommendation to check also with the Qwt mailing list.

Possibly you hook to a problem of versions. Qwt had to be updated for Qt 5 for instance.