QwtPlot derived class

Hello,

I want to create a class based upon QwtPlot. I declare it as usual:

Code:

---

#include <Qwt/qwt_plot.h>
 
class myplot : public QwtPlot{
    Q_OBJECT
 
public:
    explicit myplot(QWidget *parent = 0);
 
signals:
 
public slots:
 
};

---

But I get the error:

"During startup program exited with code 0xc0000005".

I know it's an access violation error. But I don't know why it happens only if I create a class derived from QwtPlot. In my application there are several Qwt items and all works fine.

What I should do to find (and fix) the issue?
Thanks in advance
Marco

ps. I get the same behavior if I include the incrementalplot for example

you could debug and search the code that is responsible for thisaccess violation.

could you copy your *.cpp?
no errors for me in the declaration

This is usually a problem of your build/runtime environment and has nothing to do with the code.

Uwe

Quote:

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Originally Posted by FelixB

you could debug and search the code that is responsible for thisaccess violation.

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I wrote: "During startup [...]". That means no code is executed (better, no code visible through debug).

Quote:

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Originally Posted by desantossierra

could you copy your *.cpp?
no errors for me in the declaration

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No code in the cpp file, but the empty implementation of the constructor:

Code:

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myplot::myplot(QWidget *parent): QwtPlot(parent) { }

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I've just found I need to remove the Q_OBJECT macro. Without it runs.

Does anyone know why?

Quote:

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Originally Posted by Uwe

This is usually a problem of your build/runtime environment and has nothing to do with the code.

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Maybe. But why removing the Q_OBJECT macro it works? It seems code related.

Usually because your build environment doesn't handle moc and the generated cpp files properly.

Uwe

Quote:

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Originally Posted by Uwe

Usually because your build environment doesn't handle moc and the generated cpp files properly.

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Anyway, this happens only with Qwt. I have several classes that uses Q_OBJECT without problem.
How to handle moc and cpp files properly?

So that moc is called, whenever the header changes, and the generated cpp file gets compiled and linked.

Uwe

Isn't this the default behavior? In fact, all classes I write but the Qwt-derived ones work.

Quote:

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Originally Posted by Marco Trapanese

Isn't this the default behavior?

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It depends on your IDE - f.e. MSVC has never heard of something like moc.

Uwe

QtCreator 2.4.0

O.k. this one should be fine.

What did you write in your project file: "CONFIG += qwt" ( using a proper installation following the advices from INSTALL ) or did you set the compiler/linker flags manually ?

Uwe

In my pro file I have the following entry:

Code:

---

CONFIG(debug, debug|release) {
    LIBS += -lqwtd
    DESTDIR = debug
} else {
    LIBS += -lqwt
    DESTDIR = release
}

---

I thank you for your patience.

No compiler flags - then you missed to set QWT_DLL.

Uwe

Ok, I will investigate further on that.

I had the same issue and I solved it with the advices of this topic: http://www.qtcentre.org/threads/4454...le-auto-import

Quote:

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I compiled qwt 6.0.1 dynamic library with qt 4.7.4, and added it to my qt project,
but there is a linking warning saying missing --enable-auto-import option,
I checked the qmake.conf file in mkspecs/win32-g++, QMAKE_LFLAGS is empty,
QMAKE_LFLAGS =
but in qt 4.7.3, QMAKE_LFLAGS = -enable-stdcall-fixup -Wl,-enable-auto-import -Wl,-enable-runtime-pseudo-reloc
so I added the -Wl,-enable-auto-import to qt 4.7.4, it worked.

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