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2291 :: C wrapper problem (Windows / Linux)

• matkuki (orginal) [2016-05-31T09:34:59+02:00] view original

  Hi guys,

  I've got a C wrapper procedure:

  type
    Body* = ptr object
    BB* = object
      l*: Float
      b*: Float
      r*: Float
      t*: Float
    Float* = cdouble
  
  proc newBoxShape*(body: Body; box: BB; radius: Float): PolyShape {.cdecl, importc: "cpBoxShapeNew2".}
  Run

  The C code that the above declaration wraps is this:

  typedef double cpFloat;
  
  typedef struct cpBB{
          cpFloat l, b, r ,t;
  } cpBB;
  
  cpShape *cpBoxShapeNew2(cpBody *body, cpBB box, cpFloat radius)
  {
      printf("%f", radius) // <- INSERTED BY ME TO SEE WHAT'S GOING ON
      return (cpShape *)cpBoxShapeInit2(cpPolyShapeAlloc(), body, box, radius);
  }
  Run

  When calling the newBoxShape proc in Nim like this:

  var shape = newBoxShape(
      body=body,
      box=newBB(-30.0, -30.0, 50.0, 50.0),
      radius=10.0
  )
  Run

  the value of radius in the C 'printf' function call when compiled with MinGW64-GCC 5.2.0 is 0.0, but it should be 10.0! The body and the box parameters are correct, though.

  This seems to be a Windows specific problem, as it was tested on Linux and it worked. I've tried this on Windows Vista 64-bit and Windows XP 32-bit with the same result. Nim compiler in both cases is:

  Compiler Version 0.13.1 (2016-05-29) [Windows: i386]
  Run

  GCC:

   MinGW-64 5.2.0 (x86)
  Run

  Also tested it with the MSVC 2010 compiler (x86), but then the 'printf' function call is -30.0 ???

  Any Ideas?

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• Araq (orginal) [2016-05-31T09:57:34+02:00] view original

  Use the .bycopy pragma for the BB object.

  http://nim-lang.org/docs/manual.html#foreign-function-interface-bycopy-pragma

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• matkuki (orginal) [2016-05-31T10:09:04+02:00] view original

  That's it :) ! Thanks Araq!

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