Question

I have a following lines of code:

public static string getTrack1(string track1, int len)
{
  IntPtr track1Ptr = UnsafeNativeMethods.Decrypt(track1, len);
  Byte[] track1b = new Byte[200];
  Marshal.Copy(track1Ptr, track1b, 0, track1b.Length);
   return track1b.ToString();
}

deceleration of decrypt method is :

internal static class UnsafeNativeMethods
{
  [DllImport(_dllLocation, CallingConvention = CallingConvention.Cdecl)]
  public static extern IntPtr Decrypt(string track1, int dataLen);
 }

I am returning unsigned char* from visual c++ code and whenever i am calling the dll from c# code it always returns “System.Byte[]” instead of value. Am i doing something wrong here in marshal?

please help me here

Answer 1

You’re missing the transformation from byte[] to string, but you’ll have to define what’s the encoding. This may work:

public static string getTrack1(string track1, int len)
{
  IntPtr track1Ptr = UnsafeNativeMethods.Decrypt(track1, len);
  Byte[] track1b = new Byte[200];
  Marshal.Copy(track1Ptr, track1b, 0, track1b.Length);
   return Encoding.Default.GetString(track1b);
}

But it would be better to do this;

public static string getTrack1(string track1, int len)
{
  IntPtr track1Ptr = UnsafeNativeMethods.Decrypt(track1, len);
  return Marshal.PtrToStringAnsi(track1Ptr);
}

If the encoding is Ansi (=Default)