[Info-vax] GKS : gopwk problem with VSI's version of GKS

[Joukj]

Arne Vajhøj wrote:
> On 3/17/2021 1:06 PM, Craig A. Berry wrote:
>> My Fortran is awfully rusty, but if the intent is to pass a NULL
>> pointer, wouldn't the second argument need to be %VAL(0) rather than 0?
> 
> Yes. Fortran default to BYREF for integers - not BYVAL.
> 
> $ type c.c
> #include <stdio.h>
> #include <string.h>
> 
> void m(const char *s)
> {
>     if(s == NULL)
>     {
>         printf("s = NULL\n");
>     }
>     else
>     {
>         printf("s len = %d\n", strlen(s));
>     }
> }
> 
> $ cc c
> $ type f.for
>       program f
>       external m
>       call m(%val(0))
>       call m(0)
>       call m(%ref('ABC'))
>       end
> $ for f
> $ link f + c
> $ run f
> s = NULL
> s len = 0
> s len = 3
> $
> 
> Arne
> 

I got it solved: I realy had to reboot (I thought OpenVMS was not 
Windows(#$%^&@)). So simply remove old GKS, install new GKS and rerun 
@sys$startup:gkstartup is not enough; in that case you will end-up in a 
"mixed version of old/new.


Indeed, Fortran passes all parameters by-reference, except character 
strings which are passed by-descriptor. (unless you specify %ref() or 
%val()).

In case of gopwk it seems that passing 0, %val(0) and FB_DEF_LUN 
(defined in sys$library:gks.f) all work to get the default.