Using static member variables.

[Gaminic]

Hello,

Since a number of previous "How do I solve my globals?" topics, I've gone the OOP-ish way of programming. And I've ran into my first problem.

The problem instance data is saved into a class ("Instance"). It features a series of static member variables, such as instance size. Since this will stay the same throughout the runtime, I made it static. Also, it allowed me to easily access it from other classes that need the variable.

Now, after a bit of reorganizing, my Instance class has a member structure that provides an interface to a large (linearized) matrix. This requires one of the static variables. Since it is part of the Instance class, I thought this wouldn't be a problem, but it turns out it is:

1>Instance.obj : error LNK2001: unresolved external symbol "public: static unsigned int Instance::n" (?d@Instance@@2IA)

Obvious solution? Remove the static and risk some insignificant memory waste of double parameters.

1>instance.h(37): error C2327: 'Instance::n' : is not a type name, static, or enumerator
1>instance.h(37): error C2065: 'n' : undeclared identifier

The line in question looks like this:
inline unsigned operator()(const int &i, const int &j) const { return dists[i*n+j]; }
(In the static version, I replace 'n' with 'Instance::n').

The inclusion-order is pretty simple right now: Main includes one file, which includes Instance.h. Anyone who sees where the problem is?

[Gaminic]

Apparently, the problem resides in a function of Instance() that uses the statics.

void Instance::read() {
// ...
sline >> n; // Extracts 'n' from a stringstream 

Replacing 'n' with 'Instance::n' doesn't seem to help. I'd have thought the class itself would be able to use it.

[clanmjc]

Can you display how you declared this variable? Is the class in which it resides a singleton?

[Gaminic]

It's simply a member variable of the Instance class:

class Instance
{
public:
	static nsize n; // 'nsize' is typedef'd as an unsigned int	
// ... 

[clanmjc]

It's simply a member variable of the Instance class:

I figured this much. This is silly but have you tried initializing the static variable inside the cpp?

[Gaminic]

...awkward. I did not. I figured it would happen automa(t/g)ically. I've added an initialization in the main.cpp and it seems to be working now.

Thanks!

[clanmjc]

If it was a constant you could in the header, but since it is not a constant you would need to put it in a source file. If initialization is in a header for a non const you will get a copy in every file that includes the header, so get multiply defined symbol errors from the linker. _{(which wasn't your problem but this is just added info)}

[Gaminic]

Guess that's where my confusion came from. Never worked with non-const statics before!