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I am trying call a subroutine in a Fortran DLL that requires 3 mutable strings passed to it. The subroutine is of the form:

Subroutine Getinfo(string_1, string_2, string_3, index)
char *60 string_1, string_2
char *30 string_3

string_1 = "String 1 return value"
string_2 = "String 2 return value"
string_3 = "String 3 return value"

end subroutine

Im calling the function in python as follows:

dll = ctypes.windll.LoadLibrary('library.dll')
funcprot = getattr(dll, 'Getinfo')
funcprot.argtypes = [ctypes.c_char_p, ctypes.c_long, ctypes.c_char_p, ctypes.c_long, 
     ctypes.c_char_p, ctypes.c_long, ctypes.c_long]

string_1 = ctypes.create_string_buffer(60)
string_2 = ctypes.create_string_buffer(60)
string_3 = ctypes.create_string_buffer(30)

funcprot(string_1, 60, string_2, 60, string_3, 30, 701)

I get the following error.

WindowsError: exception: access violation reading 0x000002BD

I tried suggestions from this post, but it didn't help.

What am I doing wrong? Thank you for your help.

Improve this question
8
  • See my comment on your other question. Try it as funcprot(string_1, string_2, string_3, 2, 60, 60, 30), i.e. append the lengths. Commented May 16, 2014 at 21:54
  • @eryksun Thanks for the suggestion. I will try it out as an alternative. I think I figured out the reason for the error. It was because I passed the last parameter index by value and not as reference. Changing funcprot(string_1, 60, string_2, 60, string_3, 30, 2) to funcprot(string_1, 60, string_2, 60, string_3, 30, ctypes.byref(2)) fixed the issue. I keep forgetting that in Fortran, most everything is a pointer! Commented May 18, 2014 at 16:18
  • Right, but I don't see why it would access 0x2BD (701) in this case. Anyway, if possible you should export a platform C ABI. Otherwise these ABI issues will drive you bonkers. Commented May 18, 2014 at 18:26
  • Possibly because the index value that I was trying to pass was 701. And it got interpreted as the address. Commented May 18, 2014 at 18:41
  • Can you elaborate on what you mean by "export a platform C ABI? " Commented May 18, 2014 at 18:43
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