Separate declaration and definition of static member functions

[h9uest]

Hi All:

I'm trying to declare my class in a header file.

class MyClass
{
   static int i;
public:
   static void setInt(int k);
};

Then I do the following definition of setInt in a separate cpp file.

void MyClass::setInt(int k)
{
   i = k;
};

I've also made sure that I have included the header file in the function definition cpp file.

But I am getting link error, saying can't find object or something alike. I looked it up, and found "static" has internal linkage.

So my question is, how do I work around this? I don't want to define my static function in header file.

Thanks

[ne555]

About compile errors http://www.cplusplus.com/forum/articles/40071/#msg216270

You need to define the static members.
In my_class.cpp int MyClass::i; //initial value if you want

[h9uest]

Thanks for the reply!

Sorry that I didn't provide the link error:
my_class.obj : error LNK2001: unresolved external symbol "private: static int Base::i"

Obviously, in my_class.cpp, the instruction "i=k" can't access the static data member i of MyClass.

You need to define the static members.
In my_class.cpp int MyClass::i; //initial value if you want

Yeah, your solution works.
One further question about your solution: if the int MyClass::i; is the definition of my static member, does that mean static int i; in my_class.h is only a declaration? Then I'm a bit confused: a variable in C++ needs only declaration, doesn't it? Why do we need definition of a data member?

Thanks.

[h9uest]

One more thing to double-check:

If I have a few more classes derived from MyClass, they will all have int i because they are derived from MyClass; However, since int i is static in the base class MyClass, all the derived classes will hence share the same int i, won't they?

[ne555]

In your .h you only tell how is the class. You don't construct anything there.

Yes, I think that all the derived will share it. That was an issue here http://www.cplusplus.com/forum/general/27880/

[h9uest]

Beeeaaaauuuutiful!
Thanks for the link, dude.