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4465 :: Calling stdcall from .dll

• lightern (orginal) [2018-12-12T15:10:12+01:00] view original

  Hi,

  I'm trying to build a setup in which I could write .dll libraries that I could call from excel. Now, I've managed to make it work with C. There I have two files:

  1. excelfunctions.c:

  #include <math.h>
  
  double _stdcall square (double *x)
  {
          return *x * *x;
  }
  Run

  And 2) excelfunctions.def

  LIBRARY "excelfunctions"
  EXPORTS
  squarec = square
  looperc = looper
  Run

  When I compile that with this command, everything works fine and I can call the functions from excel:

   /LD /O2 excelfunctions.c /DEF excelfunctions.def
  Run

  However with Nim, I can't get it to work. I'm not going to show all the iterations I have gone through, but here's one. Currently I have one file, excelnim.nim:

  import math
  
  proc square*(x_ptr: pointer): float64 {.stdcall,exportc.} =
    var x = cast[ptr float64](x_ptr)[]
    return x * x
  Run

  And I'm trying to compile that with:

  c --app:lib --nomain -d:release excelnim.nim
  Run

  File compiles fine, but Excel tells me that file does not exist (Excel's general error message when something goes wrong with the dll).

  I tried to include the .def file, but couldn't find how to do that from compiler manual, forums nor numerous discussions I've been reading through. But I have a lead!

  I was comparing how the dll files compare when I open them up with DLL Export Viewer. I can see the functions nicely when I'm opening the dll file I created with C compiler (cl), but when I open the file my nim code compiled into, I can only see NimMain. This is extra confusing since I'm using --nomain in my options...

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• awr (orginal) [2018-12-12T20:12:38+01:00] view original

  You're missing {.dynlib.}

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• Ward (orginal) [2018-12-13T01:11:22+01:00] view original

  https://nim-lang.org/docs/manual.html#foreign-function-interface-dynlib-pragma-for-export

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• awr (orginal) [2018-12-13T11:03:09+01:00] view original

  AFAIK the --noMain doesn't mean "don't generate NimMain()". You still need to NimMain() to boot the GC, execute top-level module code, etc.

  I believe what the flag actually does is prevent NimMain() being called in DllMain(), so you have to call NimMain() manually.

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• lightern (orginal) [2019-01-03T20:21:29+01:00] view original

  Thanks, I changed my code a bit and used {.dynlib.} and it worked! Here's the code I'm using:

  import math
  
  proc square*(x: float64): float64 {.stdcall,exportc,dynlib.} =
    return x * x
  Run

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