symbol lookup error when using plugins

[macbeth]

Hello!

I'm trying to make an application which should be extensible using (lower-level, as guys from Trolltech call it) plugins.

I want to access the methods of my own classes in the plugin, which is a source of my problems. I can access methods of Qt classes in a plugin (if they are passed as a parameter), but I can not use methods of my class (although it is passed as a parameter, too).

When I found out that sth is wrong with the plugin system, I tried to modify the Plug&Paint example (to make sure if I didn't mess up sth with plugins), but that didn't work neither.

so here is what I have in a header file:

class myClass : public QObject {
	Q_OBJECT
	public:
		int sayHello(int a);
};

class myClass : public QObject {
	Q_OBJECT
	public:
		int sayHello(int a);
};

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and the in a cpp file:

#include "myClass.h"
 
int myClass::sayHello(int a){
			a += 30;
			return a;
}

#include "myClass.h"

int myClass::sayHello(int a){
			a += 30;
			return a;
}

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I'm using slightly modified interfaces.h:

...
class FilterInterface
{
public:
    virtual ~FilterInterface() {}
 
    virtual QStringList filters() const = 0;
--> virtual QImage filterImage(const QString &filter, const QImage &image, myClass &cla, QWidget *parent) = 0;
};
...

...
class FilterInterface
{
public:
    virtual ~FilterInterface() {}

    virtual QStringList filters() const = 0;
--> virtual QImage filterImage(const QString &filter, const QImage &image, myClass &cla, QWidget *parent) = 0;
};
...

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and in the plugin code (basictools.cpp):

QImage BasicToolsPlugin::filterImage(const QString &filter, const QImage &image, myClass &cla, QWidget * /* parent */)
{   int b = 50;
--> int a = cla.sayHello( b );
    QImage result = image.convertToFormat(QImage::Format_RGB32);

QImage BasicToolsPlugin::filterImage(const QString &filter, const QImage &image, myClass &cla, QWidget * /* parent */)
{   int b = 50;
--> int a = cla.sayHello( b );
    QImage result = image.convertToFormat(QImage::Format_RGB32);

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Everything compiles fine, but I get an error at runtime (when invoking a filter):

symbol lookup error: /home/.../bin/plugins/libpnp_basictools_debug.so: undefined symbol: _ZN7myClass8sayHelloEi

symbol lookup error: /home/.../bin/plugins/libpnp_basictools_debug.so: undefined symbol: _ZN7myClass8sayHelloEi

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I've looked up here on the forum, but I didn't find a topic about it, so could you please help me or just a post a link where sth like this is explained?

Thanx.
PS: I think it is the same problem as had a guy here, but nobody replied to him...:/
PS2: Compiling on Slack 10.2 with gcc 3.3.6 and Qt 4.1.3