DLLImport System.NullReferenceException

  • Thread starter Thread starter richard.brenner
  • Start date Start date
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richard.brenner

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.
 
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.
Click to expand...

Hi. The problem didn't come from this methods. I've found the problem.
 
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