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4999 :: dynamic lib works properly when interfacing with python, fails with nim

• okapi210 (orginal) [2019-07-10T02:08:11+02:00] view original

  I have a dll with the following function signatures (Delphi):

  
  function OpenDataFile(FileName: PChar): int32;
  procedure CloseDataFile(Handle: int32);
  Run

  where OpenDataFile should return a value >= 0 on success.

  In python this works great:

  
  import ctypes
  
  dll = ctypes.WinDLL("readfile.dll")
  
  fhandle = dll.OpenDataFile(r"C:\Users\okapi210\files\test.file")
  print(fhandle)
  dll.CloseDataFile()
  Run

  returns 0

  However in nim I can't seem to get things working properly:

  
  proc OpenDataFile(filename: cstring): cint {.stdcall, dynlib: "readfile.dll", importc.}
  proc CloseDataFile(handle: cint) {.stdcall, dynlib: "readfile.dll", importc.}
  
  var fhandle = OpenDataFile(r"C:\Users\okapi210\files\test.file")
  echo fhandle
  CloseDataFile(fhandle)
  Run

  returns -1001

  nim compiler info:

  
  Nim Compiler Version 0.20.0 [Windows: amd64]
  Compiled at 2019-06-06
  Copyright (c) 2006-2019 by Andreas Rumpf
  
  git hash: e7471cebae2a404f3e4239f199f5a0c422484aac
  active boot switches: -d:release
  Run

  same result with both gcc and vcc

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• mashingan (orginal) [2019-07-10T02:18:23+02:00] view original

  Try cdecl calling convention or others like mentioned in manual page

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• okapi210 (orginal) [2019-07-10T02:23:33+02:00] view original

  @mashingan good thought. I should have mentioned I got the same result with cdecl and safecall. The dll functions definitely use stdcall, which is the calling python uses with ctypes.WinDLL.

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• Araq (orginal) [2019-07-10T07:34:01+02:00] view original

  Delphi defaults to a register calling convention that the C compilers usually don't support. You need to use

  
  function OpenDataFile(FileName: PChar): int32; stdcall;
  procedure CloseDataFile(Handle: int32); stdcall;
  Run

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• treeform (orginal) [2019-07-10T22:35:26+02:00] view original

  How does the python's ctypes work? ctypes supports register calling convention?

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• Araq (orginal) [2019-07-10T23:36:00+02:00] view original

  It could also be something else, of course. But ctypes could get lucky with the stack layout and Nim doesn't.

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• okapi210 (orginal) [2019-07-11T03:57:35+02:00] view original

  Yeah I jumped the gun... after some further testing it was just luck python was returning a 0. @Araq it's a closed source dll to make this even more annoying, but the functions are being exported as stdcall as far as I've been told.

  I set up this test. Delphi dll code:

  
  library wrapd;
  
  uses
     System.SysUtils;
  
  {$R *.res}
  
  function OpenDataFile(FileName: PChar): int32; stdcall;
  begin
    WriteLn(FileName);
    WriteLn('test test test');
    Result := 99;
  end;
  
  exports OpenDataFile;
  
  end.
  Run

  nim code:

  proc OpenDataFile(filename: cstring): int32 {.stdcall, dynlib: "wrapd.dll", importc.}
  
  let fpath: cstring = r"C:\Users\okapi210\Desktop\test.file"
  var fhandle = OpenDataFile(fpath)
  echo fhandle
  Run

  result:

  
  ?????????????????e
  test test test
  99
  Run

  So passing a cstring to PChar isn't working I probably just need a byte array

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