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6613 :: some questions on generating dynamic library

• oyster (orginal) [2020-07-29T11:13:57+02:00] view original

  I have some question, any hints? Thanks

  1. how to kill the nimMain in generated DLL, or in other way, how to do not export nimMain in DLL?

  2. Should I call NimMain? I have searched and found that Araq said "You need to also call NimMain at startup, generated by Nim" <https://forum.nim-lang.org/t/5318#33385>. But, at least for my python code, there is no difference no matter I call NimMain or not

  import ctypes
  
  DLL = ctypes.CDLL('a.dll')
  
  #~ DLL.NimMain()
  
  print(DLL.add(10, 29))
  Run

  3. how to export a variant in nimlang to DLL? I can't write

  
  const
      ver* {. exportc, dynlib.}= "2020"
  Run

  else nim says

  
  R:\a.nim(4, 22) Error: cannot attach a custom pragma to 'ver'
  
  Run

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• elcritch (orginal) [2020-07-30T03:14:30+02:00] view original

  What I found is that Nim code can (sometimes) be run from other code without calling NimMain, however, it results in random breakage. Any code dealing with constants or other items requiring initialization will break (printing floats for example). So your DLL code may not need NimMain if it's carefully written, but much better to call it on library load. Others will know about the Python library side of things.

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• snej (orginal) [2020-07-30T08:02:56+02:00] view original

  A “const” really only exists at compile time; it’s not something you can export. Try using “let” instead.

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• Yardanico (orginal) [2020-07-30T08:04:29+02:00] view original

  Also by the way, do you know https://github.com/yglukhov/nimpy exists?

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• oyster (orginal) [2020-07-30T12:53:23+02:00] view original

  no matter let or var is used, no variable is exported in the DLL. yes, I know nimpy can be used to write PYD, but it has nothing to do with a common DLL.

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• Yardanico (orginal) [2020-07-30T12:55:03+02:00] view original

  It's generally not possible to "export" a variable in a DLL, no matter the language. You need to make a function which will return that variable.

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