__init unresolved external when using C library structs converted with dstep

[Steven Schveighoffer]

On 4/14/20 2:29 PM, Robert M. Münch wrote:
> On 2020-04-14 18:23:05 +0000, Steven Schveighoffer said:
> 
>> On 4/14/20 1:51 PM, Robert M. Münch wrote:
>>> I use a C libary and created D imports with dstep. It translates the 
>>> C structs to D structs.
>>>
>>> When I now use them, everything compiles fine but I get an unresolved 
>>> external error:
>>>
>>> WindowsApp1.obj : error LNK2019: unresolved external symbol 
>>> "myCstruct.__init" (_D7myCStruct6__initZ) referenced in function _Dmain
>>>
>>> Any idea what this is about and how to fix it? I'm wondering why D 
>>> tries to find the __init function in the C library and not compile it 
>>> from the import.
>>>
>>
>> __init is not a function, it's a static member variable. It's the 
>> `intializer` property inside TypeInfo used for initialization.
> 
> Ah, ok. That's why the problem went (temporarly) away when I did a: 
> myCstruct a = {0,0}; for example?

I don't know what causes it to be emitted when. Sometimes it doesn't 
make a whole lot of sense to me.

> 
>> Did you extern(C) the struct?
> 
> Yes, everything is "extern(C) :" for the complete import files.

Then apparently the compiler still expects to have initializers even for 
foreign language structs. This is not a huge issue though, as the 
structs are ABI compatible even if compiled in D.

> 
>> Are you compiling the D file that contains the struct definition as well?
> 
> No. Is that the missing part?
> 

Probably. I think the compiler expects whatever is compiling the 
imported file to provide the symbol. If you aren't compiling it 
separately, then you need to include it in the compilation.

-Steve