Je comprends enfin...
I accidentally came across a StackOverflow answer that suggested the String
object is immutable. That makes perfect sense, as I know the C function is
actually /*trying*/ to write to the buffer.
That gave me the idea to use a ByteArray instead. Now, everything works!
horrido wrote
> There is shockingly very little documentation on how to use uFFI. In
> particular, I have the following situation...
>
> A shared C lib has the following function:
>
> void get_machine(char *machine) {
> uname(&uname_s);
> strcpy(machine, uname_s.machine);
> }
>
> It copies the content of a string value into the buffer passed to it (char
> *machine).
>
> I want to call this function from Pharo, thus:
>
> buffer := String new: 64.
> self ffiCall: #( void get_machine(String buffer) ).
>
> The buffer never receives the string value (it just contains the 64
> initiialized spaces).
>
> Clearly, I'm misunderstanding the proper mechanism for doing this.
>
> [There are other functions in the shared C lib that work fine, such as:
>
> uint get_uptime() {
> sysinfo(&info);
> return info.uptime;
> }
>
> Returning integers or floats is no problem. But passing arguments by
> reference seems to be verboten.]
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