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Putting class and main in one file

cppmatt (37)
I have a class which works fine when I use a separate header file, class file, and main file. However, I was told I needed to put the class file and main file together, but I cannot figure out what is wrong. I keep getting an error:

error LNK2001: unresolved external symbol "private: static int Circle2D::numberOfCircles" (?numberOfCircles@Circle2D@@0HA)


Here is the combined file (class defn. and main):


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#define PI 3.14159265
#include "Math.h"
#include <iostream>
using namespace std;
#include <string>

// This is the Circle2D class.
class Circle2D
{
public:

	// Construct a circle object - DEFAULT no arg.
	Circle2D()
	{
		radius = 1;
		x = 0;
		y = 0;
		cName = "Circle";
               numberOfCircles++;
	}

	// Return the number of circle objects
	static int getnumberOfCircles()
	{
		return numberOfCircles;
	}

	// Destruct a circle object
	Circle2D::~Circle2D()
	{
		numberOfCircles--;
	}

private:	
	double x, y; // The coords of center of circle.
	double radius;  // The radius of the circle.
	string cName; // The name of the circle.
	static int numberOfCircles; // Store the number of circles.
};



// Here we are going to test the Circle2D class.
int main()
{
	// Create a circle of radius on at origin.
	Circle2D *pC1 = new Circle2D(); 
	// Create a circle of radius 5 at origin.
	Circle2D *pC2 = new Circle2D();

	cout << Circle2D::getnumberOfCircles() << endl;

	// clean up.
	delete pC1;
	delete pC2;

	return 0;
}




When I was using three files it was like this:
In the header file, I had a public function declaration like this:

static int getnumberOfCircles();

and a private data member:

static int numberOfCircles;

Then in the class file, I had:

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#include "Circle2D.h"
int Circle2D::numberOfCircles = 0;

Circle2D::Circle2D()
{
radius = 1;
x = 0;
y = 0;
numberOfCircles++
}

int Circle2D::getnumberOfCircles()
{
return numberOfCircles;
}



But when I combined the files, I cannot get rid of the error. So, what did I do wrong? I don't know where to initialize the data member numberOfCircles in the combined file, I think this is why I am getting the error.

Thank you!

Last edited on
PanGalactic (1658)
You are absolutely correct. You need a line that says int Circle2D::numberOfCircles = 0; after the class definition.
cppmatt (37)
Oh, wow! How simple is that? Thank you so much. I am a noob who has been pulling my hair out for 2 hours over this!!
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