C Language Structs Object-based programming using structs
Example
Structs may be used to implement code in an object oriented manner. A struct is similar to a class, but is missing the functions which normally also form part of a class, we can add these as function pointer member variables. To stay with our coordinates example:
/* coordinates.h */
typedef struct coordinate_s
{
/* Pointers to method functions */
void (*setx)(coordinate *this, int x);
void (*sety)(coordinate *this, int y);
void (*print)(coordinate *this);
/* Data */
int x;
int y;
} coordinate;
/* Constructor */
coordinate *coordinate_create(void);
/* Destructor */
void coordinate_destroy(coordinate *this);
And now the implementing C file:
/* coordinates.c */
#include "coordinates.h"
#include <stdio.h>
#include <stdlib.h>
/* Constructor */
coordinate *coordinate_create(void)
{
coordinate *c = malloc(sizeof(*c));
if (c != 0)
{
c->setx = &coordinate_setx;
c->sety = &coordinate_sety;
c->print = &coordinate_print;
c->x = 0;
c->y = 0;
}
return c;
}
/* Destructor */
void coordinate_destroy(coordinate *this)
{
if (this != NULL)
{
free(this);
}
}
/* Methods */
static void coordinate_setx(coordinate *this, int x)
{
if (this != NULL)
{
this->x = x;
}
}
static void coordinate_sety(coordinate *this, int y)
{
if (this != NULL)
{
this->y = y;
}
}
static void coordinate_print(coordinate *this)
{
if (this != NULL)
{
printf("Coordinate: (%i, %i)\n", this->x, this->y);
}
else
{
printf("NULL pointer exception!\n");
}
}
An example usage of our coordinate class would be:
/* main.c */
#include "coordinates.h"
#include <stddef.h>
int main(void)
{
/* Create and initialize pointers to coordinate objects */
coordinate *c1 = coordinate_create();
coordinate *c2 = coordinate_create();
/* Now we can use our objects using our methods and passing the object as parameter */
c1->setx(c1, 1);
c1->sety(c1, 2);
c2->setx(c2, 3);
c2->sety(c2, 4);
c1->print(c1);
c2->print(c2);
/* After using our objects we destroy them using our "destructor" function */
coordinate_destroy(c1);
c1 = NULL;
coordinate_destroy(c2);
c2 = NULL;
return 0;
}
