Is it possible to add a static variable to a C++ struct?

Question

I am getting the following error when trying to add a static variable to my struct:

Undefined Symbole s2::aa in module file_name.cpp

s2 is the name of the structure and aa is the static variable. The compiler I am using is Turbo C++ 3.0.

How do I fix this error?

Answer 1

Static variable isn't allowed in structs in C because C requires the whole stucture elements to be placed together. To get an element value from a structure you count by the offset of the element from the beginning address of the structure.

However as far as I know you can have a static member in a C++ structure. Are you getting a specific error (which compiler?)

Answer 2

Why do you say this? Under g++ 4.1.2, this compiles:

#include <iostream>

struct Test
{
   static int test; // declare (usually in header file)
};

int Test::test = 8; // define (usually in source file)

int
main()
{
   std::cout << Test::test << std::endl;
   return 0;
}

Answer 3

Static variables are allowed in C++ structs (as you say, they are just classes with a different default access specifier).

Static variables are not allowed in C structs, however.

Answer 4

This works...

typedef struct _X
{
    static int x; // declare (usually in header file)
} X;

int X::x = 1; // define (usually in source file)

void _tmain(int argc, _TCHAR* argv[])
{
    printf("%d", X::x);
}

Answer 5

I think you've probably forgotten to define the storage for the static variable:

int C::v = 0;