Edward Bartolo <edb...@gmail.com> writes:
> Is it possible to use classes and objects while using gtk2/3? I
> noticed that only functions are used and that class use is ovoided by
> prepending functions with a group string. As far as I know, C can
> still use structs that are attached to a set of data and a set of
> functions, but without inheritance and polymorphyism.
C structs can be embedded into each other which means they can 'inherit'
other structs, eg, for a totally contrived example
struct something {
int number0, number1;
};
struct another {
struct something parent;
int drei;
};
Assuming
struct another *pa
the elements of the embedded struct can now be accessed as
pa->parent.number0
and a this pointer can be casted to a struct something * pointing at the
first member which can thus be passed to functions expecting such a
pointer as an argument.
Further, the relatively puny "polymorphism support" of Pascal or C++ is
easily implemented without help from the compiler. One can create
structures of function pointers like this
struct something_vtable {
int (*calc)(struct something *);
};
embed a pointer to that into the structure. Derived 'classes' can have
their own vtable structures and hence, supply alternate functions to
execute.
This mechanism as certain tendency make C++ developers go bezerk with a
particular type of strong rage, but it's entirely usuable in practice,
although more work than having it all laid out for oneself.
Working example:
------------
#include <stdio.h>
/* metainformation */
struct something;
struct something_vtable {
int (*calc)(struct something *);
};
/* something */
struct something {
struct something_vtable *vt;
int number0, number1;
};
static int calc_something(struct something *sth)
{
return sth->number0 + sth->number1;
}
static struct something_vtable sth_vt = {
.calc = calc_something
};
static void init_something(struct something *sth, int n0, int n1)
{
sth->vt = &sth_vt;
sth->number0 = n0;
sth->number1 = n1;
}
static int calc(struct something *sth)
{
return sth->vt->calc(sth);
}
/* another */
struct another {
struct something parent;
int drei;
};
static int calc_another(struct something *sth)
{
struct another *ath = (void *)sth;
return ath->drei + calc_something(sth);
}
static struct something_vtable ath_vt = {
.calc = calc_another
};
static void init_another(struct another *ath, int n0, int n1, int d)
{
init_something((void *)ath, n0, n1);
ath->parent.vt = &ath_vt;
ath->drei = d;
}
/* example program */
void print_result(struct something *sth)
{
printf("Result: %d\n", calc(sth));
}
int main(void)
{
struct something sth;
struct another ath;
init_something(&sth, 1, 2);
init_another(&ath, 1, 2, 3);
print_result(&sth);
print_result((void *)&ath);
return 0;
}
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