unresolved external symbol C++ Embedded

Question

I have been stuck a few days now on this issue, and I cannot find an answer to my problem even though google is fuul of replies it seems like this is quite an abstract problematic.

Here is my code in H:

struct DISPLAYLINE_t {
         char  *text;
         bool isWhite;
         void set(char *txt, bool iswhite){text = txt; isWhite = iswhite;};
};

struct DISPLAY {   
    static DISPLAYLINE_t line1,line2,line3,line4; 
    void clear(){//dostuff};
};

When I try to access from my Main:

DISPLAY::line1.set(string, FALSE);

I get the following error:

error LNK2019: unresolved external symbol "public: static struct DISPLAYLINE_t DISPLAY::line1" (?line1@DISPLAY@@2UDISPLAYLINE_t@@A) referenced in function WinMain

Any ideas?

Answer 1

You have to provide a definition at global namespace scope for your static data members (at least for those that you are odr-using in your code):

DISPLAYLINE_t DISPLAY::line1;
DISPLAYLINE_t DISPLAY::line2;
DISPLAYLINE_t DISPLAY::line3;
DISPLAYLINE_t DISPLAY::line4;

This live example shows how you should fix your program.