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

[vuott at tutanota.com]

Hello,
sorry, I can't see in libgpiod header file, indicated by you, where and how the functions, which return a data of type Structure, set the error code to the `errno`. Am I missing something?


5 ott 2022, 05:46 da matheus at castello.eng.br:

> 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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