Re: New VSI post on Youtube

On 8/23/2024 9:02 AM, Arne Vajhøj wrote:

On 8/23/2024 4:14 AM, Michael S wrote:

                    and that the best option in C is the same
as in many other languages - return the structure itself.

 Returning the struct itself result in a copy of the struct. The
time to do the copy is probably insignificant though.

I am not quite convinced yet.

It seems like one frequently provided reason for using pointer
is ABI compatibility.
I don't know about that. It is not that easy to create the
problem.
But it is possible:
$ type i.h
struct data
{
     int a;
     int b;
#ifdef NEWVERSION
     int c;
#endif
};
$ type s1.c
#include "i.h"
struct data get()
{
     struct data res;
     res.a = 123;
     res.b = 456;
#ifdef NEWVERSION
     res.c = 0x7FFFFFFF;
#endif
     return res;
}
$ type m1.c
#include <stdio.h>
#include  "i.h"
struct data get();
int main()
{
     struct data res = get();
     printf("%d %d\n", res.a, res.b);
     return 0;
}
$ type s2.c
#include <stdlib.h>
#include "i.h"
struct data *get()
{
     struct data *res = malloc(sizeof(struct data));
     res->a = 123;
     res->b = 456;
#ifdef NEWVERSION
     res->c = 0x7FFFFFFF;
#endif
     return res;
}
$ type m2.c
#include <stdio.h>
#include <stdlib.h>
#include  "i.h"
struct data *get();
int main()
{
     struct data *res = get();
     printf("%d %d\n", res->a, res->b);
     free(res);
     return 0;
}
$ cc s1
$ cc m1
$ link m1 + s1
$ run m1
123 456
$ cc/define="NEWVERSION" s1
$ link m1 + s1
$ run m1
99108 0
$ cc s2
$ cc m2
$ link m2 + s2
$ run m2
123 456
$ cc/define="NEWVERSION" s2
$ link m2 + s2
$ run m2
123 456
Arne