Undefined reference to static variable and static method

Question

#include <iostream>
using namespace std;

class Assn2
{
  public:
     static void set_numberofshape();
     static void increase_numberofshape();

  private:         
      static int numberofshape22;
};

void Assn2::increase_numberofshape()
{
  numberofshape22++;
}

void Assn2::set_numberofshape()
{
  numberofshape22=0;
} // there is a problem with my static function declaration

int main()
{
  Assn2::set_numberofshape();
}

Why do I get an error undefined reference to Assn2::numberofshape22 when I compile this?

I am trying to declare an static integer :numberofshape22 and two methods.

Method 1 increase numberofshapes22 by 1

Method 2 initialise numberofshape22 to 0

What am I doing wrong ??

harper · Accepted Answer · 2013-10-20 14:44:20Z

4

You just declared the variable. You need to define it:

int Assn2::numberofshape22;

answered Oct 20, 2013 at 14:44

harper

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Comments

Pierre Fourgeaud · Accepted Answer · 2013-10-20 14:56:43Z

2

The declaration of a static data member in the member list of a class is not a definition.

To respect the one Definition Rule you must define a static data member. In your case you only declared it.

Example:

// in assn2.h
class Assn2
{
  // ...
  private:         
      static int numberofshape22; // declaration
};

// in assn2.cpp

int Assn2::numberofshape22; // Definition

edited Oct 20, 2013 at 14:56

answered Oct 20, 2013 at 14:50

Pierre Fourgeaud

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