[Gambas-user] Get last errno from external function call

[Bruce Steers]

Is errno global to the application or the entire system?
I would imagine just the application.

I would also imagine the gambas error system works independent of the
libraries one?

How to get the libraries errno I do not know, sorry.

Good luck
BruceS

On Wed, 5 Oct 2022, 05:09 Matheus Castello, <matheus at castello.eng.br> wrote:

> For example some calls from libgpiod return structs, if the return is a
> null pointer then you have an error. For this cases libgpiod set the
> error code to the `errno` and you need to read it as soon the function
> returns the null pointer.
>
> Reference:
>
> https://git.kernel.org/pub/scm/libs/libgpiod/libgpiod.git/tree/include/gpiod.h#n28
>
>
> On 10/5/2022 12:25 AM, Jussi Lahtinen wrote:
> > You mean an error occurring inside the library? I don't think there is
> > any other way, than the library itself reporting the error code.
> > I don't see why using __errno_location inside the library would fail.
> > Are you calling it from the Gambas code?
>
> Yeah, I add an `External` declaration to it to try to get the errno, but
> as I said "surely the runtime (I mean the Gambas3 runtime) must be
> making other calls that are overwriting the errno" and I'm always
> getting `errno = 0` that means success.
>
> .NET for example have an annotation to store the errno from an external
> function the `SetLastError`:
>
> https://github.com/dotnet/iot/blob/main/src/System.Device.Gpio/Interop/Unix/libgpiod/Interop.libgpiod.cs#L49
>
> I was looking for something similar in Gambas3.
>
> BR,
> Matheus Castello
>
>
> > If this is about a missing error message, then are you reading it from
> > stderr?
> > You need to give more details and/or some code to see.
> >
> > Jussi
> >
> >
> >
> >
> > On Wed, Oct 5, 2022 at 5:54 AM Matheus Castello <matheus at castello.eng.br
> > <mailto:matheus at castello.eng.br>> wrote:
> >
> >     Hi guys,
> >
> >     I'm new to Gambas3, I'm trying to use it for embedded devices and I'm
> >     doing some external function calls. There is some way in Gambas3 to
> >     get,
> >     or Gambas runtime stores, the last errno from a external function
> call?
> >
> >     I tried to get it directly from libc `__errno_location` but surely
> the
> >     runtime must be making other calls that are overwriting the errno.
> >
> >     Thanks in advance,
> >     Matheus Castello
> >
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> >
> >
> >
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