Separating class code into a header and cpp file

c++ oop class
drdrdr picture drdrdr · Mar 6, 2012 · Viewed 312.1k times · Source

I am confused on how to separate implementation and declarations code of a simple class into a new header and cpp file. For example, how would I separate the code for the following class?

class A2DD
{
  private:
  int gx;
  int gy;

  public:
  A2DD(int x,int y)
  {
    gx = x;
    gy = y;
  }

  int getSum()
  {
    return gx + gy;
  }
};

Answer

Ferenc Deak picture Ferenc Deak · Mar 6, 2012

The class declaration goes into the header file. It is important that you add the #ifndef include guards, or if you are on a MS platform you also can use #pragma once. Also I have omitted the private, by default C++ class members are private.

// A2DD.h
#ifndef A2DD_H
#define A2DD_H

class A2DD
{
  int gx;
  int gy;

public:
  A2DD(int x,int y);
  int getSum();

};

#endif

and the implementation goes in the CPP file:

// A2DD.cpp
#include "A2DD.h"

A2DD::A2DD(int x,int y)
{
  gx = x;
  gy = y;
}

int A2DD::getSum()
{
  return gx + gy;
}

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