> Hi There.
>
> I try to implement methos from an unmanaged DLL in C# to get access to
> an external device.
> I have a problem with the following C method:
>
> char* __stdcall RDR_SendCommandGetData(void* hReader, char* command,
> char* data, char* buffer);
>
> My C# counterpart:
>
> [DllImport("Reader.dll",CharSet=CharSet.Ansi,SetLastError=true)]
> internal static extern string RDR_SendCommandGetData(IntPtr hReader,
> string command, string data,StringBuilder buffer);
>
> I get an error at the following call:
>
> output=ReaderBinding.RDR_SendCommandGetData(reader,command,commandvalue,buf­fer);
>
> The error is:
> An unhandled exception of type 'System.NullReferenceException'
> occurred in testapp.exe
> Additional information: Object reference not set to an instance of an
> object
>
> In order to get and receive data, I previously have to open the Reader
> device and receive the handle.
>
> The methods are:
> C:
> void* __stdcall OpenComm(char* commDevice, char autodetect, struct
> presetSettings* settings);
>
> C#:
> [DllImport("Reader.dll",SetLastError=true,CharSet=CharSet.Ansi)]
> internal static extern IntPtr RDR_OpenComm(System.String device,int
> autodetect, presetSettings settings);
>
> call:
> IntPtr reader;
> reader=ReaderBinding.RDR_OpenComm("COM5",1,null);
>
> I tried setting some ref and out attributes but it doesn't change the
> error.
>
> Please help.
> Thanks.