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8660 :: importcpp constructor issue

• mantielero (orginal) [2021-11-27T11:26:53+01:00] view original

  I am facing the following issue. I have the following code:

  {.experimental: "codeReordering".}
  {.experimental: "callOperator".}
  include tkmath/tkmath, tkernel/tkernel
  
  let
    myWidth = 50.0
    myThickness = 20.0
    myHeight = 70.0
    aPnt1 = newPnt( (25.0).cfloat, (2.0).cfloat, (3.0).cfloat ) #newPnt((-myWidth / 2.0).cfloat, (0.0).cfloat, (0.0).cfloat)
  
  echo aPnt1.x
  Run

  where newPnt is defined as:

  proc newPnt*(xp: cfloat; yp: cfloat; zp: cfloat): Pnt {.cdecl, constructor,
      importcpp: "gp_Pnt(@)", dynlib: tkmath.}
  Run

  When compiling:

  
  nim cpp ex01
  Run

  it is generating the following:

  Run

  What am I missing?

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• haxscramper (orginal) [2021-11-27T11:56:55+01:00] view original

  I haven't fully reproduced your error, but I've faced with similar problems in the https://forum.nim-lang.org/t/8352#53847 - that is, I need to somehow link with the C++ library. From what I can understand, dynlib does not properly support C++ name mangling, or it does so in some weird manner that I can't understand.

  class WithConstructor
  {
    public:
      WithConstructor(int arg);
      WithConstructor(int arg1, int arg2);
  };
  Run

  #include "lib.hpp"
  #include <iostream>
  
  WithConstructor::WithConstructor(int arg) {
      std::cout << "Called with constructor, single argument\n";
  }
  
  
  WithConstructor::WithConstructor(int arg1, int arg2) {
      std::cout << "Called with constructor, two arguments\n";
  }
  Run

  wrapped using

  const
    h = "lib.hpp"
    l = "liblib.so"
  
  type
    WithConstructor {.importcpp: "WithConstructor", header: h.} = object
  
  proc newWithConstructor(arg: cint): WithConstructor {.
    importcpp: "WithConstructor(@)", constructor, cdecl.}
  
  proc newWithConstructor(arg: cint, arg2: cint): WithConstructor {.
    importcpp: "WithConstructor(@)", constructor, cdecl, dynlib: l.}
  
  proc main() =
    let val1 = newWithConstructor(20)
    let val2 = newWithConstructor(20, 30)
  
  main()
  Run

  generates proper constructor calls if compiled with nim r --backend:cpp --passl:-llib nim_cxx_dynlib_constructor_main.nim (where lib is a shared library compiled from the C++ code), but in order to properly work this has to be compiled with -llib, which means that you basically need to use regular dynamic linker and not dynlib.

  WithConstructor val1(((int) 20));
  WithConstructor val2(((int) 20), ((int) 30));
  Run

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• haxscramper (orginal) [2021-11-27T12:00:18+01:00] view original

  And in general I would probably wrap things using dynamic linker and not dynlib, especially when it comes to the C++, because it is not really clear what it does in this case. dynlib might seem simpler to use though, since for dynamic linker you would also need to configure the LIBRARY_PATH and LD_LIBRARY_PATH variables if you have placed your shared library in some nonstandard folder (first should be accessible at compile time so linker could work, and second one must be set up when program is actually executed)

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• mantielero (orginal) [2021-11-27T12:30:50+01:00] view original

  Thanks for the tips. I managed to make it work by replacing dynlib with header.

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