[SOLVED] Interface class - undefined reference to vtable for MyInterface

  • Hello everyone!
    I'v been trying to create an interface class in my project. Based on this "example":http://doc.qt.nokia.com/4.6/tools-plugandpaint-interfaces-h.html I'v create following class:
    #ifndef IVARIABLE_H
    #define IVARIABLE_H

    #include <QtPlugin>

    class QByteArray;
    class QString;

    class IVariable{
    virtual ~IVariable(){}
    virtual QString dataId() const;
    virtual void setDataId(QString &dataId);
    virtual QByteArray value() const;
    virtual void setValue(QByteArray &value);
    Q_DECLARE_INTERFACE(IVariable, "my.IVariable/1.0")
    #endif // IVARIABLE_H
    My problem is, that when i try to build my project where o got class Variable that implements such virtual class, I am getting following errors:
    In function '~IVariable': variable.o
    undefined reference to 'vtable for IVariable' ivariable.h 11
    In function 'IVariable': variable.o
    undefined reference to 'vtable for IVariable' ivariable.h 9
    undefined reference to 'typeinfo for IVariable' (.rodata._ZTI8Variable[typeinfo for Variable]+0x18)
    collect2:ld returned 1 exit status
    I am quite new to C++ programing. Could anyone please explain me what am I doing wrong? Thanks a lot!

  • If you define a real interface, the members must be pure virtual, which means, the yhave no implementation and that must be noted in the header:

    class IVariable{
    virtual QString dataId() const = 0;
    virtual void setDataId(QString &dataId) = 0;
    virtual QByteArray value() const = 0;
    virtual void setValue(QByteArray &value) = 0;
    virtual void changeValue(QByteArray &value) = 0;

  • That did the trick! thanks a lot!;-)

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