1.8. Defining Classes and Class Methods

Class definitions are usually placed in the header file.

Example 1.8.1

Example 1.8.1

// POINT.H

#ifndef POINTH

#define POINTH 1

class point

{

int x, y;

public:

point (int x1 = 0, int y1 = 0);

int & getx (void);

int & gety (void);

. . .

};

#endif

Because the description of the point class is planned to be included in other classes in the future, to prevent inadmissible duplication of descriptions, the conditional preprocessor directive #ifndef POINTH is included in the text. Thus, the text describing the point class can appear in the compiled file only once, despite the possibility of the repeated appearance of #include “point.h” directives.
Methods can be defined as follows.

// POINT.CPP
#ifndef POINTCPP
#define POINTCPP 1
#include “point.h”
point:: point (int x1, int y1) {x = x1; y = y1;}
int & point:: getx (void) {return x;}
int & point:: gety (void) {return y;}
. . .
#endif
In a program using class objects
#include “point.cpp”
. . .
void main (void)
{
point A (5,6);
point B (7,8);
. . .
}

The external definition of class methods makes it possible, without changing the interface of class objects with other parts of programs, to implement component functions in different ways.