Initializing static variables in static function result in unresolved

Question

class PossibilisticShellClustering
{
public:
    PossibilisticShellClustering(void);
    ~PossibilisticShellClustering(void);
    static void SetParameters(double deltaDistance);
    static  double deltaDistance
};

and i wanto to initialize static variable deltaDistance in function SetParameters. So in *.cpp file I wrote

void PossibilisticShellClustering::SetParameters(double deltaDistance)
{
    PossibilisticShellClustering::deltaDistance = deltaDistance;    
}

however I get linker erros

unresolved external symbol "public: static double PossibilisticShellClustering::deltaDistance" (?deltaDistance@PossibilisticShellClustering@@2NA)

Could somebody tell me why ?

PossibilisticShellClustering.obj

You have no semi-colon after static double deltaDistance?

Oliver Charlesworth
– Oliver Charlesworth

2011-04-30 22:40:12 +00:00
Commented Apr 30, 2011 at 22:40 — Oliver Charlesworth
– Oliver Charlesworth, Commented Apr 30, 2011 at 22:40

Lara Bailey · Accepted Answer · 2011-04-30 22:40:48Z

2

You need to defined PossibilisticShellClustering::deltaDistance in a source file somewhere in your program, usually a .cc or .cpp file.

double PossibilisticShellClustering::deltaDistance;

What you have in the class body (or would have if it was terminated with a ;) is only a declaration. Static data members also need a definition.

answered Apr 30, 2011 at 22:40

Lara Bailey

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5 Comments

user2100815 Over a year ago

And explicitly initialise it, I would say.

Lara Bailey Over a year ago

@unapersson: It will be zero-initialized first and as he's writing a function for later explicit assignment, unless he has a special value that it needs to have during start up and explicit initializer seems a bit redundant.

user2100815 Over a year ago

I hate coming across statics that aren't initialised and then wondering if the guy that created them really wanted them to be default initialised to zero, or just forgot to initialise them to what they should be. Explicit initialisation only takes a few keystrokes, after all.

Lara Bailey Over a year ago

@unapersson: I hate coming across statics. ;-) Enforcing explicit initialization of statics even if you wanted the zero-initialized default is not something I can bring myself to care about greatly. Anyone who manages to forget to initialize a static to some non-zero value that actually matters needs to test their code more thoroughly IMHO.

user2100815 Over a year ago

Well, I have to disagree here. A good static analysis tool (or even a compiler) can detect non-explicitly initialised statics and IMHO should do so - after all, where's the loss? I agree that in the great scheme of things it probably is not Error #1, but if it is one more thing that can go wrong, why not diagnose it?

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