I'm developing for Windows, 64-bit at the moment with MSVC and DMD. I have this C code file, config.c:

    #define STRINGIZE( x ) STRINGIZE_( x )
    #define STRINGIZE_( x ) #x

    const xu16 ocoCoreVerMajor   = _MILES_VER_MAJOR;
    const xu16 ocoCoreVerMinor   = _MILES_VER_MINOR;
    const xu16 ocoCoreVerPatch   = _MILES_VER_PATCH;
    const char* ocoCoreVerBuild  = STRINGIZE( _MILES_VER_BUILD );
    const char* ocoCoreTimestamp = STRINGIZE( _MILES_BUILD_TSTAMP );

And for D code, I have this interface, config.d:

    module oco.core.config;

    extern (C) const ushort ocoCoreVerMajor;
    extern (C) const ushort ocoCoreVerMinor;
    extern (C) const ushort ocoCoreVerPatch;
    extern (C) const char* ocoCoreVerBuild;
    extern (C) const char* ocoCoreTimestamp;

The linker gives me this error:

    [ÔÇô/debug] Linking         oco...
    [ÔÇô/debug stop] config.d.obj : error LNK2005: ocoCoreVerMajor already defined in
    config.c.obj
    ...
    [ÔÇô/debug stop] C:\Users\Alex\AppData\Local\Temp\miles-build\oco.exe : fatal error LNK1169: one or more multiply defined symbols found
    [ÔÇô/debug stop]

I figure the D code is defining symbols redundantly, and they're not weakly defined, so this happens. Obviously I can't exactly just hand the definitions into D, as you can see by the C code this is actually the best way to pass these values around across language boundaries (there are a few). How do I tell D to treat this right?

On Thursday, 20 December 2018 at 08:17:58 UTC, Alexander Nicholi wrote:
>
>     extern (C) const ushort ocoCoreVerMajor;
>     extern (C) const ushort ocoCoreVerMinor;
>     extern (C) const ushort ocoCoreVerPatch;
>     extern (C) const char* ocoCoreVerBuild;
>     extern (C) const char* ocoCoreTimestamp;

Mark these as external, so extern(C) extern const ...

On Thursday, 20 December 2018 at 08:17:58 UTC, Alexander Nicholi wrote:
> I'm developing for Windows, 64-bit at the moment with MSVC and DMD. I have this C code file, config.c:
>
> [...]

This belongs in the Learn forum:

https://forum.dlang.org/group/learn

See the docs on interfacing to C globals, you need the additional `extern` storage class:

https://dlang.org/spec/interfaceToC.html#c-globals
https://dlang.org/spec/declaration.html#extern

On Thursday, 20 December 2018 at 08:27:55 UTC, Dennis wrote:
> On Thursday, 20 December 2018 at 08:17:58 UTC, Alexander Nicholi wrote:
>>
>>     extern (C) const ushort ocoCoreVerMajor;
>>     extern (C) const ushort ocoCoreVerMinor;
>>     extern (C) const ushort ocoCoreVerPatch;
>>     extern (C) const char* ocoCoreVerBuild;
>>     extern (C) const char* ocoCoreTimestamp;
>
> Mark these as external, so extern(C) extern const ...

Oh, that works fine, thanks. I thought I already did that with the extern (C), but I guess that's a different kind of extern isn't it

On Thursday, 20 December 2018 at 08:31:53 UTC, Alexander Nicholi wrote:
> Oh, that works fine, thanks. I thought I already did that with the extern (C), but I guess that's a different kind of extern isn't it

Indeed, extern(C) only changes the mangled name and calling convention, it doesn't also mark variables as extern.