Class in C (not C++) - c

Question

I've discovered this hack in a website in Spanish (http://trucosinformaticos.wordpress.com/2010/12/12/programacion-orientado-a-objetos-en-c/).
I want create a "class" in C (not C++), but when I compile, I obtain the next errors:
source.c(25): warning C4047: 'function' : 'Car' differs in levels of indirection from 'Car *'
source.c(25): warning C4024: 'changeYears' : different types for formal and actual parameter 1
This is my code:
#include <string.h>
typedef struct Car* Car;
// class Car
// {
struct Car
{
int years;
//char model[100];
};
void changeYears(Car this, int years)
{
this->years = years;
}
// }
int main(void)
{
Car my_cars[10];
//nombrar(mis_alumnos[0], "Pepito");
changeYears(&my_cars[0], 6); // My car has now 6 years
return 0;
}

Answer 1

I would agree with #Oli Charlesworth that hiding a pointer behind a typedef is a very easy way to confuse yourself and others.
However, to make your code compile and work, you can just remove the & operator in front of my_cars. You also need to allocate memory for those pointers. I would say the reason why you made this mistake in the first place was that you confused yourself with the pointer hiding.
#include <string.h>
typedef struct Car* Car;
struct Car
{
int years;
//char model[100];
};
void changeYears(Car this, int years)
{
this->years = years;
}
int main(void)
{
// An array of struct char*
Car my_cars[10];
int i;
for (i = 0; i < 10; i++)
my_cars[i] = malloc(sizeof(struct Car));
changeYears(my_cars[0], 6); // My car has now 6 years
return 0;
}
Here is a more reasonable way to implement this without hiding pointers.
#include <string.h>
typedef struct
{
int years;
//char model[100];
} Car;
void changeYears(Car* this, int years)
{
this->years = years;
}
int main(void)
{
Car my_cars[10];
changeYears(&my_cars[0], 6); // My car has now 6 years
return 0;
}

Answer 2

I think this is what you are looking for:
(A much cleaner implementation, of what you want)
CODE:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
typedef struct
{
int years;
} Car;
void changeYears(Car *this, int years)
{
this->years = years;
}
int main(void)
{
Car *car = malloc(sizeof(Car));
changeYears(car, 2014);
printf("car.years = %d\n", car->years);
free(car);
return 0;
}
OUTPUT:
car.year = 2014