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5809 :: exportc pragma and ref object

• jdn (orginal) [2020-01-13T23:36:35+01:00] view original

  When I compile the following code:

  import strutils
  
  type
    Token {.exportc.} = object
      typ: cint
      val: cstring
  
  proc exportc(a: Token) {.exportc.} =
    let msg = "Token (type, value): ($1, $2)" % [$a.typ, $a.val]
    echo msg
  Run

  with

  
  nim c --header exportc.nim
  Run

  I get a header file with the following snippet:

  typedef struct Token Token;
  struct Token {
  int typ;
  NCSTRING val;
  };
  N_NOCONV(void, signalHandler)(int sign);
  N_NIMCALL(NI, getRefcount)(void* p);
  N_NIMCALL(void, exportc)(Token a);
  N_CDECL(void, NimMain)(void);
  Run

  which is what I expect and can then call from a c main function. However, if I change the object to a ref object

  
    Token {.exportc.} = ref object
      typ: cint
      val: cstring
  Run

  I get a header file with the following:

  typedef struct tyObject_TokencolonObjectType___My6xn9bSiVikjAjVy7Y8xcA tyObject_TokencolonObjectType___My6xn9bSiVikjAjVy7Y8xcA;
  N_NOCONV(void, signalHandler)(int sign);
  N_NIMCALL(NI, getRefcount)(void* p);
  N_NIMCALL(void, exportc)(tyObject_TokencolonObjectType___My6xn9bSiVikjAjVy7Y8xcA* a);
  N_CDECL(void, NimMain)(void);
  Run

  So for a ref object the exportc pragma doesn't stop name mangling which makes calling from c a pain. Is this a bug or is there something about reference objects I'm not comprehending.

  Thanks,

  Jason

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• mratsim (orginal) [2020-01-14T12:42:05+01:00] view original

  It's a bug, you can report it on Github: https://github.com/nim-lang/Nim/issues/new/choose

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• Araq (orginal) [2020-01-14T15:28:38+01:00] view original

  There is little point in exporting a ref object though.

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• mratsim (orginal) [2020-01-14T16:59:15+01:00] view original

  They could be opaque objects in C. Though their memory management would be somewhat tricky.

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• jdn (orginal) [2020-01-14T17:59:53+01:00] view original

  So does that mean there is no way to export a recursive type to C++/C? I'm happy to make a bug report if this is considered an issue.

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• Araq (orginal) [2020-01-14T18:28:31+01:00] view original

  "Nim recursive type" has nothing to do with this, the point is that ref is under Nim's memory management control, for C interop use ptr.

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• Araq (orginal) [2020-01-14T18:43:48+01:00] view original

  Also and more importantly, --header is unsupported, write your header files manually or extract them via a 3rd party tool.

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• jdn (orginal) [2020-01-14T20:01:37+01:00] view original

  Got it, I was assuming this was going to be less effort on my part, thank you. I was using the --header flag mostly to see how to make the interface. Also, all material I could find on how to call nim from C uses it.

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• Lachu (orginal) [2021-11-27T12:24:38+01:00] view original

  Few minutes ago I asks for the same problem on this forum. I will generate header and add my own, which include generate header and creates aliases for types. I hope the way nim mangles names will not be changed in future.

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