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3401 :: Wrap C++ procedure / Parameter type float / shared library

• dodo11 (orginal) [2017-12-06T23:09:18+01:00] view original

  Hello, I like to set up a "Jester" (example.nim) to handle some data transmitted by a httpRequest and using a shared library (calc.so) made with C++ to do some calculation on the data before sending it back to client.

  The Header file calc.h that seems to be necessary for nim-compilation looks like follows.

  #include <vector>
  std::vector< std::vector<float> > calculation(float paramOne, float paramTwo);
  Run

  For wrapping C++ and getting request-data I use the following syntax in Nim, which compiles without error.

  import asyncdispatch, jester, strutils
  
  type vector {.importcpp: "std::vector", header: "<vector>".} [T] = object
  proc calculation(paramOne: cfloat, paramTwo: cfloat): vector[vector[cfloat]] {.importcpp: "calculation", header: "../calc.h".}
  
  routes:
    
    get "/":
      redirect "index.html"
    
    get "/request":
      let requestData = request.params
      let requestOne = requestData["one"].parseFloat
      let requestTwo = requestData["two"].parseFloat
      
      #some additional Nim code
  
  runForever()
  Run

  But if using the imported procedure with following syntax I get a compilation error.

  let result = calculation(requestOne, requestTwo)
  Run

  Error: execution of an external compiler program 'clang++ -c  -w  -I/Users/developer/nim/nim-0.17.0/lib -o /Users/developer/Documents/Example/src/nimcache/Example_example.o /Users/developer/Documents/Example/src/nimcache/Example_example.cpp' failed with exit code: 1
  
  /Users/developer/Documents/Example/src/nimcache/Example_example.cpp:830:66: error: member reference base type 'float' is not a structure or union
                                  (*colonenvP_).result8 = ((float) ((*colonenvP_).requestOne6)).calculation(((float) ((*colonenvP_).requestTwo7)));
                                                          ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~
  Run

  By the way, I am doing "nimble cpp src/example.nim" to compile.

  Has anybody an idea how to do it right?

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• dom96 (orginal) [2017-12-07T00:39:05+01:00] view original

  Try importc, importcpp assumes the first parameter is a class instance.

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• dodo11 (orginal) [2017-12-07T18:42:43+01:00] view original

  Unfortunately there is also an error when using "importc".

  So I will check how to implement the interface between Nim and C++ with class instance as first parameter. ...the shared library will be modified related to Nims needs :)

  Thanks so far!!

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• dodo11 (orginal) [2017-12-07T22:59:36+01:00] view original

  Actually "importc" is working well. I just missed to tell Nim the direction to the shared library.

  So adding {.link: "cpp/calc.so".} and using either importc: "calculation" or importcpp: "calculation(@)" seems to be the solution.

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