unresolved references when using static

[Tony Johansson]

Hello!

I have the two classes Outdoors and Animal and a main. The Outdoors class is
a singleton.
The Outdoors is in outdoors.h and Animal is in animal.h. I'm using .h file
just for being easy to show you.
You can see the definition of the classes below.

Now to my problem in the instance method of class Outdoors I call
the static method makeAnimal(); which have only one statement and that is
this temp = new Animal();
The definition of temp is located in the private section and looks like
static Animal* temp;
When I have this temp = makeAnimal() statement it will not compile. I get
the following errors.

Compiling...
start.cpp
Linking...
start.obj : error LNK2001: unresolved external symbol "private: static class
Animal * Outdoors::temp" (?temp@Outdoors@@0PAVAnimal@@A)
Debug/slask.exe : fatal error LNK1120: 1 unresolved externals
Error executing link.exe.

Why can't I instansiate an object of class Animal.?

start.cpp
*******
#include "outdoors.h"
int main()
{
Outdoors* base = Outdoors::instance();
return 0;
}

outdoors.h
*********
class Outdoors
{
public:

static Outdoors* instance()
{
if (onlyInstance == 0)
{
onlyInstance = new Outdoors();
makeAnimal();
}
return onlyInstance;
}
private:
static Animal* temp;
static Outdoors* onlyInstance;
Outdoors() {}

static void makeAnimal()
{ temp = new Animal(); }
};
Outdoors* Outdoors:nlyInstance = 0;
//end outdoors.h
*************

animal.h
**********
class Animal
{
public:
Animal() {}
private:
};

Many thanks!
//Tony

 

[Rade]

You should have defined Outdoors::temp just the same way you have defined
Outdoors:nlyInstance:

Animal *Outdoors::temp = 0;

Think of moving the definitions to a cpp file (see my previous post).

Rade