[Ovmsdev] Bitfields and C Compilers

[Mark Webb-Johnson]

My 2c is that I switched to #defines when I did that work on net.h some time ago. It looks quite neat and works well.

Regards, Mark.

On 7 Feb, 2013, at 10:33 AM, Tom Saxton wrote:

> on 2/6/13 1:55 PM, Michael Balzer wrote:
> 
>> thanks for the info... I'll change the bit fields back to #defines, had
>> those in the first place but thought bit fields were meant for this kind
>> of job.
> 
> Bitfields are a nice feature of the language and are intended for exactly
> this purpose, at least for runtime structures.
> 
> I am opposed to this sort of thing:
> 
> car_doors1 |= 0x0c;     // Set charge and pilot bits
> 
> Magic numbers are bad, especially when they have hidden maintenance issues.
> 
> Language constructs with self-explanatory names are good. Defined constants
> with self-explanatory names are almost as good.
> 
> For bitfields that define data passed between different programs, equivalent
> to a binary file format, which thus have to be identical at the bit level
> across different compilers, processors and platforms, defined constants are
> probably best. You can make compiler-based bitfields work by using a program
> to generate a header file with the bitfields in the right order for that
> build's compiler, but that's probably more hassle than is appropriate for
> this project.
> 
> For bitfields that are for runtime only and not passed between programs,
> using the language-defined bitfields is preferable to named constants as
> they are easier to maintain.
> 
>    Tom
> 
> 
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