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10284 :: how to make a dll in nim-lang?

• ploxotnuj1 (orginal) [2023-06-19T09:27:49+02:00] view original

  I have a problem with dll files, I noticed one oddity if I compile this code

  
  proc helloWorld(): string {.exportc, dynlib.} =
    return "Hello World
  Run

  and compile and then try to run the dll in python or another programming language, then everything is fine, but as soon as you need to give an argument to the function

  
  proc hello(slovo: string): string {.exportc, dynlib.} =
    echo slovo
  Run

  and run like this in python

  
  import ctypes
  lb = ctypes.cdll.LoadLibrary("./main.dll")
  result = lb.hello("Hello World")
  print(result)
  Run

  then prints

  
  out of memory
  Run

  how to solve this problem?

  p.s. libraries for compatibility with python are not suitable. I want to be able to call a function from a dll, for example on rust or golang

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• pietroppeter (orginal) [2023-06-19T09:56:36+02:00] view original

  you could use genny to generate a c dll (will not support GC): https://github.com/treeform/genny

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• Calonger (orginal) [2023-06-19T10:06:29+02:00] view original

  string != cstring . Use cstring no string

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• ploxotnuj1 (orginal) [2023-06-19T10:27:07+02:00] view original

  thank you, IT WORKS, but for some reason only one letter is displayed:

  import ctypes
  lb = ctypes.cdll.LoadLibrary("./main.dll")
  result = lb.hello("LOL")
  print(result)
  Run

  proc hello(slovo: cstring): cstring {.exportc, dynlib.} =
    echo slovo
  Run

  
  python main.py
  L
  Run

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• SpotlightKid (orginal) [2023-06-19T11:43:26+02:00] view original

  You need to pass a byte string from the Python side:

  import ctypes
  lib = ctypes.cdll.LoadLibrary('./libhello.so')
  lib.hello(b"Hello World!")
  Run

  Also, your Nim function should probably return void instead of cstring.

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• sls1005 (orginal) [2023-06-19T11:45:59+02:00] view original

  Because you are using a Python string instead of bytes or bytearray.

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• sls1005 (orginal) [2023-06-19T11:57:46+02:00] view original

  Another problem is that the string wasn't referenced by any living Python variable, thus could be freed.

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