Passing array of character arrays to Fortran from C#

Question

I am attempting to call the following FORTRAN method:

subroutine MYMETHOD(THEARRAY)

with the parameter

CHARACTER*200  :: THEARRAY(2)

This seems simple enough but I ran into trouble because it is an array of character arrays. I have tried several approaches to this including marshaling (which runs in to problems because there are multiple strings.) The best I can come up with is:

[DllImport("theFortranDLL.dll", CallingConvention = CallingConvention.Cdecl)]
static extern void MYMETHOD(THEARRAY);

static void Main(string[] args)
{
    StringBuilder[] theArray = new StringBuilder[2];

    theArray[0] = new StringBuilder("DataA",200);
    theArray[1] = new StringBuilder("DataB",200);

    MYMETHOD(theArray);
}

However, this does not work. How would I call such a method from C#? Thanks!

Just tried it. The program I run it in produced the same output as my code here does. My code does run but FORTRAN complains when the data comes in. I think the data is arriving in a form FORTRAN wasn't expecting. — chessofnerd
– chessofnerd, Commented Mar 14, 2013 at 3:51
Just tried that as well. No luck ): I have tried string[], string on its own, StringBuilder[], and StringBuilder on its own also some ref's with string[], etc. Does my code as it stands look correct? If so, I might be barking up the wrong tree. I don't currently have access to the FORTRAN's source code so it's possible the C# code is correct. The method is calling: it gets into the FORTRAN code and FORTRAN is printing a program specific warning that suggests the incoming data wasn't what it expected. — chessofnerd
– chessofnerd, Commented Mar 14, 2013 at 4:02

M. S. B. · Accepted Answer · 2013-03-14 06:01:45Z

1

In Fortran, CHARACTER*200 :: THEARRAY(2) is not an array of arrays. It is a two element array of scaler strings of length 200. In other languages it might be an array of arrays. Each Fortran string is padded on the end with blanks. I don't know how C# handles strings ... C terminates strings with a null character. For Fortran, that null character would have to be replaced with blanks, all the way to position 200.

answered Mar 14, 2013 at 6:01

M. S. B.

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