Chapter 1. Object Lessons

In C, a data abstraction and the operations that perform on it are declared separately—that is, there is no language-supported relationship between data and functions. We speak of this method of programming as procedural, driven by a set of algorithms divided into task-oriented functions operating on shared, external data. For example, if we declare a struct Point3d, such as the following:

typedef struct point3d 
{ 
   float x; 
   float y; 
   float z; 
} Point3d; 

the operation to print a particular Point3d might be defined either as a function

void 
Point3d_print( const Point3d *pd ) 
{ 
   printf(”( %g, %g, %g )”, pd->x, pd->y, pd->z ); 
} 

or, for efficiency, as a preprocessor macro:

 #define Point3d_print( pd ) \ printf(”( %g, %g, %g )”, ...

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