Question

I have some simple hypothetical static class in C++:

#ifndef __STAT_H_
#define __STAT_H_

class Stat {

 private:
  static vector<int> v;

 public:

  static void add_num(int num);
  static void clear_nums();
  static void get_count();
};

#endif

And the ccp file is so:

#include "Stat.h"

vector<int> v;


void Stat::add_num(int num) {
  v.push_back(num);
}

void Stat::clear_nums() {
  v.clear();
}

int Stat::get_num_count() {
  return v.size();
}

Now when I include in main.cpp file “Stat.h” and try to use some static method:

Stat::add_num(8);

the error during compilation is

undefined reference to ‘Stat::add_num(int)’

What can be the problem in this case? Thank you.

EDIT: sorry about addresses vector, it should be v there

Answer 1

It sounds like you have not included stat.cpp in compilation. So your linker cannot find an implementation for the static methods.