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Re: Irritating multiple redefinition problem -- please help

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David Brown <david.brown@hesbynett.no> writes:

> On 14/09/15 14:39, August Karlstrom wrote:
>> On 2015-09-14 10:24, David Brown wrote:
>>> On 14/09/15 05:50, Ian Collins wrote:
>>>> Make the declaration in the header
>>>>
>>>> extern const double PI2;
>>>>
>>>> and define in in one and only one .c file
>>>>
>>>> const double PI2 = 6.28;
>>>>
>>>
>>> Alternatively, especially for simple constants, change the declaration
>>> in the header file to the definition :
>>>
>>> static const double PI2 = 6.28;
<snip>
>> Why not simply
>> 
>>     #define PI2 6.28
>
> Yes, that would work too in this case.  But there is a general trend
> that if something can be expressed as a typed constant value, rather
> than a pre-process macro, then the const is to be preferred.  It has
> better type safety, can be scoped (not relevant in this case), is less
> prone to accidents (because you can only use it in places where that
> type is appropriate), and plays better with IDEs/editors and
> debuggers.

You mention twice safety twice, but 6.28 (the result of the #defined)
has the same type as PI2 defined as a const double.  The latter is an
lvalue (though not a modifyable one) but that's probably not important.

<snip>
-- 
Ben.

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Irritating multiple redefinition problem -- please help dakupoto@gmail.com - 2015-09-13 20:39 -0700
  Re: Irritating multiple redefinition problem -- please help Ian Collins <ian-news@hotmail.com> - 2015-09-14 15:50 +1200
    Re: Irritating multiple redefinition problem -- please help David Brown <david.brown@hesbynett.no> - 2015-09-14 10:24 +0200
      Re: Irritating multiple redefinition problem -- please help August Karlstrom <fusionfile@gmail.com> - 2015-09-14 14:39 +0200
        Re: Irritating multiple redefinition problem -- please help David Brown <david.brown@hesbynett.no> - 2015-09-14 15:45 +0200
          Re: Irritating multiple redefinition problem -- please help Richard Heathfield <rjh@cpax.org.uk> - 2015-09-14 14:52 +0100
            Re: Irritating multiple redefinition problem -- please help August Karlstrom <fusionfile@gmail.com> - 2015-09-14 18:13 +0200
          Re: Irritating multiple redefinition problem -- please help Ben Bacarisse <ben.usenet@bsb.me.uk> - 2015-09-14 16:41 +0100
          Re: Irritating multiple redefinition problem -- please help dakupoto@gmail.com - 2015-09-14 19:47 -0700
            Re: Irritating multiple redefinition problem -- please help Paul N <gw7rib@aol.com> - 2015-09-15 16:00 -0700
  Re: Irritating multiple redefinition problem -- please help gordonb.78i5t@burditt.org (Gordon Burditt) - 2015-09-13 23:40 -0500
  Re: Irritating multiple redefinition problem -- please help Ike Naar <ike@iceland.freeshell.org> - 2015-09-20 20:24 +0000

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