[gpm] Check return codes everywhere

[Markus Elfring]

> Jep, it will stay C.
>   

It's a pity. I guess that the completion of error handling will need
more efforts in this case.
A mixture of elements from the C and C++ programming languages would be
nice to benefit from exceptions in function implementations. I assume
that it should be clearer which parts belong to the public API and ABI
details.


> I am not sure what you mean by that.

The aspect-oriented term "pointcut" means filters for function interfaces.
The tool "Coccinelle" provides also filtering capabilities on source code..

I suggest to consider that software tools can find the places in the
source files for us where adjustments should be applied.

Regards,
Markus