Passing C# function from C++ unmanaged dll

Question

I have device with C++ DLL interface and I should create C# class to control it. I have no problem with (dis)connecting to this device, but I could not get read function :

Definiton of function in interface is :

bool Driver_Read(int DeviceNo, unsigned char *pReadBuf, unsigned long ReadLen, unsigned long *pReadLen)

I did som research, and I have found that this code should work :

[DllImport("..\\..\\..\\..\\Driver.dll")]
public static extern bool Driver_Read(int deviceNo, StringBuilder pReadBuf, ulong readLen, ref UInt32 pReadLen);

But when I run it, I get an AccessViolationException : "Attempted to read or write protected memory. This is often an indication that other memory is corrupt."

Lots of people had similar problem, but nothing was helpful for me. Do you know, where could be the problem? Thanks in advance.

it looks like `pReadLen` is needed to figure out how long the string is. You can't just do a direct `StringBuilder` conversion like that. — Scott Chamberlain, Jan 20 '14 at 15:33
I don't know, I know enough PInvoke to know what is wrong, but not enough to fix it. — Scott Chamberlain, Jan 20 '14 at 15:36
Have a look at this: http://stackoverflow.com/questions/13991060/unsigned-char-equivalent-in-c-sharp-and-have-to-write-the-return-value-in-a-f — Jorge Córdoba, Jan 20 '14 at 15:37
When I use IntPtr instead of StringBuilder, it says that it doesnt match unmanaged target signature. — eduard, Jan 20 '14 at 15:43
"unsigned long" is not ulong. You already knew that because it got it right for the 4th argument. — Hans Passant, Jan 20 '14 at 18:56

Idov · Answer 1 · 2014-01-20T18:37:28.030

0

try this:

[DllImport("..\\..\\..\\..\\Driver.dll")]
public static extern bool Driver_Read(int DeviceNo, IntPtr pReadBuf, uint ReadLen, ref uint pReadLen)

this should help with the conversions of types from C++ to C#:
http://msdn.microsoft.com/en-us/library/ac7ay120(v=vs.110).aspx

edited Jan 20 '14 at 18:37

answered Jan 20 '14 at 18:25

Idov

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Passing C# function from C++ unmanaged dll

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