Re: [LAD] G++ trouble

On Mon, 16 Nov 2020 13:35:30 +0100
Fons Adriaensen <fons@linuxaudio.org> wrote:

>On Mon, Nov 16, 2020 at 12:22:54PM +0000, Will J Godfrey wrote:
>
>> In GCC 8.3 doing that in a globally included header actually *creates* a
>> multiple definitions error!
>>
>> #ifndef GLOBALS_H
>> #define GLOBALS_H
>>
>> const unsigned int ADD_COLOUR = 0xdfafbf00; fine
>
>Putting a definition in a header file is usually a bad idea.
>What you get from this (without 'extern' is a separate copy
>in each file that includes the header. GCC 8 will not flag
>this as an error.
>
>> extern const unsigned int ADD_COLOUR = 0xdfafbf00; boom!
>
>This normally should not create ADD_COLOUR, just tell the
>compiler that it exists somewhere. So this should result
>in an 'undefined' error.
>
>If OTOH you get a 'multiple definition' error that would
>normally mean there are other definitions as well. Maybe
>you had this in a number of files, decided later to make
>it a single global, and forgot to delete the originals ?
>
>Ciao,
>

Not wishing to hijack this thread but I'm still confused :(

I just did a search of the whole of src. It's *used* about a dozen times
across 5 otherwise unrelated .cpp files, but is only defined here. Just to be
certain, I did a make clean before trying this again, and it's definitely saying
multiple defs

e.g
/usr/bin/ld: CMakeFiles/yoshimi.dir/UI/WidgetMWSlider.cpp.o:(.rodata+0x0):
multiple definition of `ADD_COLOUR';
CMakeFiles/yoshimi.dir/Interface/InterChange.cpp.o:(.rodata+0x1840): first
defined here

This happens at the linker stage.

Also, I thought the whole idea of putting things like this in a #ifndef/#def
block was to ensure it was only set once.

-- 
It wasn't me! (Well actually, it probably was)
... the hard part is not dodging what life throws at you,
but trying to catch the good bits.
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