Hi Graeme,
> Hi Wolfgang
>
> On Wed, Nov 9, 2011 at 9:49 AM, Wolfgang Denk <w...@denx.de> wrote:
>> Dear Simon Glass,
>>
>> In message
>> <capnjgz15f_gva5+mm1em-l2smxt1waatxqikuhoqat893t9...@mail.gmail.com> you
>> wrote:
>>>
>>> This discussion was regarding the need to #ifdef the variable declaration,
>>> viz:
>>>
>>> #if defined(THING1) || defined(THING2)
>>> const char *cat;
>>> #endif
>>>
>>> ...
>>>
>>>
>>> #ifdef THING1
>>> cat = getenv("cat");
>>>
>>> send_back(cat);
>>> #endif
>>>
>>> ....
>>>
>>> #ifdef THING2
>>> cat = check_outside("cat");
>>>
>>> if (cat)
>>> wibble(cat);
>>> #endif
>>>
>>>
>>> and whether the top bit would be better as:
>>>
>>> __maybe_unused const char *cat;
>>>
>>> But more generally, lots of #ifdefs do make the code harder to read,
>>> and potentially more brittle in the face of config changes.
>>
>> I would like to see only a minimal number of "__maybe_unused" in the
>> code - in cases, where this is the way that hurts least.
>>
>> In the examples above, it might be better to use local blocks, like:
>>
>> #ifdef THING1
>> {
>> const char *cat = getenv("cat");
>>
>> send_back(cat);
>> }
>> #endif
>
> I honestly think most of these cases can be factored out into functions.
> The compiler should inline them anyway so the overhead should be zero.
> The various board.c files are a prime example of where this should be
> done as a matter of principle to reduce the complexity and lenght of
> the primary function anyway
I would even like to skip the ifdefs completely. Modern compilers with
dead code elimination will completely do away unneeded code _but still
do syntax checks on the parts every time_.
So maybe we should simply try to use
if (THING1)
{
...
}
I know that this would need an "#ifdef THING1 1" but errors in this
would be caught immediately (and not only under a certain combination of
ifdefs) by the compiler so I don't think this is a problem.
I don't know how often I repeat my mantra, but every ifdef doubles
the number of _different source codes_ that we deal with.
Cheers
Detlev
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