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

[vuott at tutanota.com]

I did a test...
Looking at the sources of the libgpiod functions, I see that in many of them a value is assigned to the "errno" symbol.
For example in the "int gpiod_line_bulk_add_line ()" function:
    errno = EINVAL;

https://git.kernel.org/pub/scm/libs/libgpiod/libgpiod.git/tree/lib/core.c#n147


Not having installed the "libgpiod" library on my system, I tried to create "ex novo" a similar function, and to test it with Gambas:

' void simula_errore()
Private Extern simula_errore() In "/tmp/liberror"


Public Sub Main()

  Dim p As Pointer

' Go to create the external shared library, that will simulate the "EINVAL" error:
  Creaso()

' Calls then  External function:
  simula_errore()

' Catch the error:
  p = System.GetExternSymbol("/tmp/liberror", "errno")
 
  Print Int@(p)

End


Private Procedure Creaso()

File.Save("/tmp/liberror.c", "#include <errno.h>\n\n" &
                               "void simula_errore() {\n" &
                               "   errno = EINVAL;\n}")

Shell "gcc -o /tmp/liberror.so /tmp/liberror.c -shared" Wait

End
------

Maybe I'm thinking wrong, in any case it works for me.

-----------------------------------------------------------------------------------
6 ott 2022, 10:43 da benoit.minisini at gambas-basic.org:

> Le 06/10/2022 à 01:30, vuott--- via User a écrit :
>
>> Out of curiosity, maybe you could also try "System.GetExternSymbol ()":
>>
>>     Dim p As Pointer
>>
>>     p = System.GetExternSymbol("libgpiod", "errno")
>>
>>     Print Int@(p)
>>
>
> Don't do that, as 'errno' is not a global variable anymore according to the glibc manual ('man errno' says it's a C macro).
>
> Regards,
>
> -- 
> Benoît Minisini.
>
>
> ----[ http://gambaswiki.org/wiki/doc/netiquette ]----
>

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