Linker errors with private members of class in header file

Question

Hi. I'm trying to build a project in Visual Studio 2008. I'm getting a bunch of linker errors that are really bothering me. My application is a Win32 console application using only native ANSI C++.

They are all linker errors of the same pattern. Linker errors are related to every single private static data member of classes I have defined in my own header files.

I'm guessing this is probably a simple fact of c++ I'm not already aware of?

Example: I refer to the members of SingleDelay within function definitions of SingleDelay's member classes in a file Delays.cpp. ie:

SingleDelay::tick(void *output, void *input, int nbufferFrames)
{ //.. code here
x = dry * castInput + wet * castInput;
}

Error 38 error LNK2001: unresolved external symbol "private: static double SingleDelay::dry" (?dry@SingleDelay@@0NA) Delays.obj testall

Definition of SingleDelay in Delays.h:

class SingleDelay{

    private:  
        static double dry; //% of dry signal<br>
        static double wet; //% of wet signal<br>
        static unsigned int delay; //Delay in milliseconds<br>
        static int delayCell; //Index in the delayBuffer of the delay to add<br>
        static double *delayBuffer; //Delay buffer is 1 second long at sample rate SAMPLE_RATE<br>
        static unsigned int bufferCell; //Pointer to the current delay buffer cell<br>

    public:

        //Tick function
        static void tick(void *output, void *input,int nBufferFrames);

        //Set and Get functions
        static void setSingleDelay(double tDry, double tWet, unsigned int tDelay);
        static void setSingleDelay(void);

        static void setDry(double tDry);
        static void setWet(double tWet);
        static void setDelay(unsigned int tDelay);

        static double getDry(){ return dry;}
        static double getWet(){ return wet;}
        static unsigned int getDelay(){ return delay;}

        static void initializeDelayBuffer(){
            destroyDelayBuffer();

            delayBuffer = new double[bufferLength];
        }
        static void destroyDelayBuffer(){
            delete[ ] delayBuffer;
        }
};

Answer 1

Are you adding the .cpp and .h files to .vcproj file?

Answer 2

1. Maybe you haven't added the library and include paths of the library you use to the project definitions?
2. C++ error are always fun to look at. Or not. In any case, do you initialize your static variables anywhere? You need to do this in a .cpp file somewhere. And remember to use static variables with care. They are actually global variables in disguise, and can make future changes, such as multi-threading, more difficult.

Answer 3

They are all linker errors of the same pattern. Linker errors are related to every single private static data member of classes I have defined in my own header files.

All static data members must have a definition in a .cpp file somewhere.

Error 38 error LNK2001: unresolved external symbol "private: static double SingleDelay::dry" (?dry@SingleDelay@@0NA) Delays.obj testall

The linker is telling you that there is no defined storage for that variable. This line must appear somewhere in exactly one .cpp file:

double SingleDelay::dry = 0.0;

Answer 4

Hi, Jun!

Maybe error consists in your static fields visibility scope, because they are private. Try write code that use your privete static field in class definition, not beyond your class. Write this method just in your class definition:

class SingleDelay{
 ...
int tick(void *output, void *input, int nbufferFrames)
{ //.. code here
x = dry * castInput + wet * castInput;
}
 ...
}