Static function pointer

Why cant I do the following:

..........................header file:
class CFPointerTest{

private:

public:
CFPointerTest();

static int (*test)();

static void setF();
static int f1();

};

..........................cpp file:
CFPointerTest::CFPointerTest(){



}

void CFPointerTest::setF(){

CFPointerTest::test= f1;

}

int CFPointerTest::f1(){

return 1;

}

........................................
It says "undefined reference to `CFPointerTest::test'"
It works when test and setF are not static.

I'm not completely sure, but it must be because of the nature of static class members.

In order to use (almost) any class member, you need to instantiate an object of that class, in which case the constructor should take care of initializing all pointer members. The exception to that rule is the static member, which does not depend on any object having been instantiated. In fact, you can still call and use a static class member even if absolutely no objects of that class exist. However, that also means that no constructor ever needs to have been called, which means that no pointers will have been initialized.

It therefore seems impossible to have a static pointer member since it could never be initialized.

For static function pointers (or for that matter, any kind of static member variable), you need to initialize them outside a method, like you're initializing a global variable:
CFPointerTest.h

CFPointerTest.cpp


That will make it work.

You need to initialize like this because a static member variable is common to all instances of a class and should be initialized always before any instances of class are instantiated.

Sorry, I dont really understand. Im no expert. How do you mean initialized? It just holds a memory adress like an int holds a number. I can assign something to a static int member(through a static function) without the constructor being called. Why is it different?
Thanks!


EDIT:
Sorry! I remember now, ...like with singletons.
(like CKeys* CKeys:Instance= 0; in the cpp)
Thanks!

The problem is not in fact one of initialisation, but rather one of instantiation. You have to create the static instance because it is independent of any single object instance.

It's for exactly the same reason as when you have a header file with you need a source file (or "compilation unit") that defines x. The header file only declares that x exists; it doesn't set aside any space for it. A static member of a class is just like that: the "static ..." declaration in the class body only declares that this member exists; it doesn't reserve any space for it (unlike a non-static member, which has space reserved for it in each instance of the class). When you define the static member in a source file and compile that file, the resulting object file will have the necessary bytes reserved for it in its data section.

Thanks! It works now.
I just dont understand that syntax.
Why this:
int (*CFPointerTest::test)() = f1;

And why not this?
int CFPointerTest:(*test)())= f1;