PInvoke issues with custom dll

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I am just playing around with some PInvoke stuff. I am getting an AcessViolationException error when I am trying to run the app. This is my C++ code"

C++

extern "C"
{
  __declspec(dllexport) double DecodeLatitude(string s, bool mustFlip)
  {
    bitset<28> hh(s);
    if (mustFlip) {hh.flip();}
    return hh.to_ulong();
  }
}

And here is my C# code that calls this:

C#

[DllImport("BinaryConvert.dll", CallingConvention = CallingConvention.Cdecl)]
        public static extern double DecodeLatitude([MarshalAs(UnmanagedType.BStr)]string s, [MarshalAs(UnmanagedType.I1)]bool mustFlip);

static void Main()
        {
            double a = DecodeLongitude("001000110010001110111001100", false);
            Console.ReadLine();
        }

Can someone help a beginner out :P

Posted 28-Nov-11 6:37am

DominicZA

Updated 28-Nov-11 10:19am

v2

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Richard MacCutchan · Answer 1 · 2011-11-28T06:49:00

Solution 1

You need to check the definitions for the different types between C# and C++. For example, UnmanagedType.LPStr as defined here[^], is a pointer to a null-terminated array of ANSI characters. This equates to a char* in C++, not a string.

Similarly, you are returning an unsigned long (hh.to_ulong()) to a C# call that expects a Double value to be returned.

Posted 28-Nov-11 6:49am

Richard MacCutchan

Comments

DominicZA 28-Nov-11 16:20pm

Please see updated code. The issue is definitely with the string. I have tested everything else, but it only crashes when I parse it a string.

Richard MacCutchan 29-Nov-11 4:48am

Did you read my comments? Your function parameter in the C++ code needs to match the type of the parameter in the C# code. You are not passing a std::string from your calling method, nor is your C++ function returning a Double.