static struct member gets “undefined reference”. Don't know why

Question

I want to create a class that collects information from many other classes and the end of a simulation. For that, it has to be independent from all other classes and completely accessible. For that I chose a static approach, a static struct indeed.

This is my Foo.h

class Foo
{
 public:
   static int app_counter;

   typedef struct
   {
       double eed;
       int bits;  
   }APPLayer;

   static APPLayer applayer_metric;
public:
   Foo(){};
   ~Foo();
};

This is the Foo.cpp

#include "Foo.h"
int Foo::app_counter=0;
//How do I set all internal members to zero?
Foo::APPLayer applayer_metric;
Foo::~Foo()
{
  std::cout << app_counter << std::endl; 
  //Which is the way to access to the values of my members?
  std::cout << applayer_metric.bits << std::endl;
}

This is the error I get in my Foo.CPP

Foo.cc:38: undefined reference to `Foo::applayer_metric'

If for instance I change the line in Foo.cpp to this one

std::cout << Foo::applayer_metric.bits << std::endl;

I get exactly the same error.

My questions are:

How can I initialize all members of a static struct variable to zero?
How do I access to these members in other functions in Foo.cpp?

FYI, there is no complain if I initialize and access the variable "app_counter"

What am I doing wrong?

Thanks in advance.

possible duplicate of [c++ undefined reference to to static member](http://stackoverflow.com/questions/9110487/c-undefined-reference-to-to-static-member) — PlasmaHH, Feb 22 '13 at 10:24
possible duplicate of [What does it mean to have an undefined reference to a static member?](http://stackoverflow.com/questions/7092765/what-does-it-mean-to-have-an-undefined-reference-to-a-static-member) — Mankarse, Feb 22 '13 at 10:27
@PlasmaHH it is not a duplicate because I define and declare the struct. I want to initialize them. The typo 'e' is now corrected — Humberto, Feb 22 '13 at 10:28

score 4 · Accepted Answer · answered Feb 22 '13 at 10:26

4

Your definition of Foo::applayer_metric is missing a scope resolution operator. Change it to this:

Foo::APPLayer Foo::applayer_metric;

answered Feb 22 '13 at 10:26

Mankarse

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sorry for the last comment. It was a typo. I think this was the last option to test! Now I can initialize the struct at the constructor, thanks a lot. I am reading your post, if I could have found it, I would have not posted this question here. :) – Humberto Feb 22 '13 at 11:04

static struct member gets “undefined reference”. Don't know why

1 Answers1