Re: New VSI post on Youtube

On 8/21/24 19:13, Arne Vajhøj wrote:

On 8/21/2024 8:26 AM, chrisq wrote:

On 8/21/24 02:25, Lawrence D'Oliveiro wrote:

On Tue, 20 Aug 2024 09:47:36 -0400, Arne Vajhøj wrote:

Few languages support multiple return values.

>
Even in C and Fortran, a function can return a struct.

>
Better to declare the struct externally, then pass a pointer
to it. Much tidier.

 In C one should definitely return a pointer to struct and not

Problem is that of you return a pointer, that suggests that the
struct has been declared static inside the called function. That
would be a fail for reentant code that might be called from
elsewhere, say, from an interrupt handler, or another thread.
The struct would  typically be on the stack or heap, and would
disappear on return from the call, making the return value
invalid. Ideally, in a multitasking os, all code should be
designed to be fully reentrant, to make it safe in all
situations.
Chris

a struct.
 It looks like VSI Fortran cannot return a structure as function
result, but VSI Pascal can return a record as function result.
 And it is returned as a pointer argument under the hood.
 $ type s.pas
module s;
 type
    iiituple = record
                  a : integer;
                  b : integer;
                  c : integer;
              end;
 [global]
function get : iiituple;
 var
    res : iiituple;
 begin
    res.a := 123;
    res.b := 456;
    res.c := 789;
    get := res;
end;
 end.
$ pas s
$ type m.c
#include <stdio.h>
 struct iiituple
{
     int a;
     int b;
     int c;
};
 void get(struct iiituple *res);
 int main()
{
     struct iiituple res;
     get(&res);
     printf("%d %d %d\n", res.a, res.b, res.c);
     return 0;
}
$ cc m
$ link m + s
$ run m
123 456 789
 Arne