expected type-specifier before 'Class Name' / not declared in this scope

[sfabel]

Hi ppl,

have a relatively straightforward problem, but can't seem to figure out what's happening here.

I've created a shared library with Qt. It compiles fine, and is installed. I try to instantiate an object from one of the defined classes in main.cpp of a program using the library.

#include <myClass.h>
 
int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
 
    ManiDialog *w = new ManiDialog( 0 );
 
    MyClass *m = new MyClass();
 
    w->show();
    return a.exec();
}

#include <myClass.h>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    ManiDialog *w = new ManiDialog( 0 );

    MyClass *m = new MyClass();

    w->show();
    return a.exec();
}

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The library is added to the .pro file, the include path is set. I've used the Q_DECL_EXPORT macro in the library (QtCreator created this automatically for me). I don't know if that is important to this. MyClass is a concrete class, whose abstract base class is also defined in the library.

class MyClass LIBMYCLASS_EXPORT : public MyOtherClass

class MyClass LIBMYCLASS_EXPORT : public MyOtherClass

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I get the following error when running "Build" in QtCreator:

main.cpp:10: error: ‘m’ was not declared in this scope
main.cpp:10: error: expected type-specifier before ‘MyClass’
main.cpp:10: error: expected ‘;’ before ‘MyClass’
make: *** [main.o] Error 1

main.cpp:10: error: ‘m’ was not declared in this scope
main.cpp:10: error: expected type-specifier before ‘MyClass’
main.cpp:10: error: expected ‘;’ before ‘MyClass’
make: *** [main.o] Error 1

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Can anyone help me out? This seems so straightforward...

Thanks,
Stephan

[tbscope]

Did you include the header file that defines MyClass?

[sfabel]

Did you include the header file that defines MyClass?

Yes. Unfortunately, I can't think of anything else that would cause this error. Interestingly enough, if I leave out the header file include, I get an additional error (can't remember right now, but something along the lines of 'undefined type 'MyClass'' or something similar).

Thanks for any help.

Stephan

[tbscope]

And the ManiDialog include?

[sfabel]

Yep, the include files are all there.

This compiles:

#include <QtGui/QApplication>
 
#include "manidialog.h"
 
int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
 
    ManiDialog *w = new ManiDialog( 0 );
 
    w->show();
    return a.exec();
}

#include <QtGui/QApplication>

#include "manidialog.h"

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    ManiDialog *w = new ManiDialog( 0 );

    w->show();
    return a.exec();
}

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This doesn't:

#include <QtGui/QApplication>
 
#include <myclass.h>
 
#include "manidialog.h"
 
int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
 
    ManiDialog *w = new ManiDialog( 0 );
 
    MyClass *m = new MyClass();
 
    w->show();
    return a.exec();
}

#include <QtGui/QApplication>

#include <myclass.h>

#include "manidialog.h"

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    ManiDialog *w = new ManiDialog( 0 );

    MyClass *m = new MyClass();

    w->show();
    return a.exec();
}

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Thanks
Stephan

[SixDegrees]

I'll note that your include file is called "myClass.h" (or "myclass.h" in your second example) while the class itself is "MyClass"; the difference in case shouldn't make any difference to the compiler, but some of the Qt tools can be fussy about such things, so it's best to be consistent.

[squidge]

Then perhaps the error is in myclass.h, so post that file.

and what is 'LIBMYCLASS_EXPORT' ?

[sfabel]

Here goes:

#ifndef MYCLASS_H
#define MYCLASS_H
 
 
#include "libmyclass_global.h"
#include "myotherclass.h"
 
 
class LIBMYCLASS_EXPORT MyClass : public MyOtherClass
{
    Q_OBJECT
 
public:
    MyClass()
    virtual ~MyClass();
 
    virtual void initialize();
    virtual void printDebug() const;
 
public slots:
    virtual void control();
};
 
#endif // MYCLASS_H

#ifndef MYCLASS_H
#define MYCLASS_H


#include "libmyclass_global.h"
#include "myotherclass.h"


class LIBMYCLASS_EXPORT MyClass : public MyOtherClass
{
    Q_OBJECT

public:
    MyClass()
    virtual ~MyClass();

    virtual void initialize();
    virtual void printDebug() const;

public slots:
    virtual void control();
};

#endif // MYCLASS_H

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MyOtherClass.h:

#ifndef MYOTHERCLASS_H
#define MYOTHERCLASS_H
 
#include <QObject>
#include <QString>
#include <QTimer>
 
#include "myclass_global.h"
 
class LIBMYCLASS_EXPORT MyOtherClass : public QObject
{
    Q_OBJECT
 
public:
    MyOtherClass( );
    virtual ~MyOtherClass();
 
    virtual void initialize();
    virtual void printDebug() const;
 
public slots:
    virtual void control() = 0;
};
 
#endif // MYOTHERCLASS_H

#ifndef MYOTHERCLASS_H
#define MYOTHERCLASS_H

#include <QObject>
#include <QString>
#include <QTimer>

#include "myclass_global.h"

class LIBMYCLASS_EXPORT MyOtherClass : public QObject
{
    Q_OBJECT

public:
    MyOtherClass( );
    virtual ~MyOtherClass();

    virtual void initialize();
    virtual void printDebug() const;

public slots:
    virtual void control() = 0;
};

#endif // MYOTHERCLASS_H

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[sfabel]

...and what is 'LIBMYCLASS_EXPORT' ?

Sorry - I don't know about that. I am using Qt Creator and started a project "shared library" when it added this, with the global include file like so:

#ifndef LIBMYCLASS_GLOBAL_H
#define LIBMYCLASS_GLOBAL_H
 
#include <QtCore/qglobal.h>
 
#if defined(LIBMYCLASS_LIBRARY)
#  define LIBMYCLASS_EXPORT Q_DECL_EXPORT
#else
#  define LIBMYCLASS_EXPORT Q_DECL_IMPORT
#endif
 
#endif // LIBMYCLASS_GLOBAL_H

#ifndef LIBMYCLASS_GLOBAL_H
#define LIBMYCLASS_GLOBAL_H

#include <QtCore/qglobal.h>

#if defined(LIBMYCLASS_LIBRARY)
#  define LIBMYCLASS_EXPORT Q_DECL_EXPORT
#else
#  define LIBMYCLASS_EXPORT Q_DECL_IMPORT
#endif

#endif // LIBMYCLASS_GLOBAL_H

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[squidge]

Your constructor seems to be missing a semicolon?

[sfabel]

Your constructor seems to be missing a semicolon?

Yeah, sorry my fault. It's there in the source.

[ChrisW67]

#include <QtGui/QApplication>
#include <myclass.h>
#include "manidialog.h"
 
int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    ManiDialog *w = new ManiDialog( 0 );
    MyClass *m = new MyClass();
    w->show();
    return a.exec();
}

#include <QtGui/QApplication>
#include <myclass.h>
#include "manidialog.h"

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    ManiDialog *w = new ManiDialog( 0 );
    MyClass *m = new MyClass();
    w->show();
    return a.exec();
}

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At line 2 you are asking the pre-processor to look for the file myclass.h in the system include directory path. This path is a compound of a built-in value and any "-I" directives (or equivalents) and typically does not include the current directory. You should be receiving a pre-processor error saying it cannot find myclass.h before you get the error message you are describing here.

Have you tried:

#include "myclass.h"

#include "myclass.h"

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The compiler will look in all the same places for the file but it will look in the current (actually same directory as the cpp file) directory first.

[sfabel]

Thank you guys for your help. In case you haven't noticed, I tried to clean up the code before posting to remove any unnecessary clutter.

However, it seems that by doing that, the error actually went away. So I will keep re-building the MyClass and MyOtherClass until the error starts to appear again. As far as I can tell, there's nothing wrong with the code I've posted so far.

(The includes are all found, per compiler directive -I/usr/local/include).

I'll get to the bottom of this, and write my findings here, so in case this happens again I don't waste another day or two finding the error.

Thanks,
Stephan