convert code snippet from VB6 to C#

[Funky]

Hello guys!

I have a code sample in VB6. I'd like to use this steps in my C# application.

The VB6 code snippet:

Public Declare Function MXReadFingerFromSensor Lib "MXOTDLL.dll" (ByRef FingerBuf As Byte) As Integer
 
Dim FingerBuf(256, 304) As Byte
 
MXReadFingerFromSensor(FingerBuf(0, 0))
 

I know how to call the function from the dll but I don't know how to create a file buffer (is it a 2d array of type of byte or else) to put it in a reference for function call because I don't know exactly what the 3th line of code does. And I have a question:
In the MXReadFingerFromSensor is the FungerBuf variable a function argument. The 0, 0 arguments tell that the MXReadFingerFromSensor function should start to fill the buffer from the begining?

Please give me an explicit example for doing this in C# so I can recive the file buffer from the function.

[balabaster]

[DllImport("MXOTDLL.dll")]
static extern int32 MXReadFingerFromSensor(byte[] FingerBuf);
 
byte[256,304] FingerBuf;
MXReadFingerFromSensor(FingerBuf[0, 0]);
 

I don't have the DLL itself, so I've got no way to test it...but that should be along the right lines.

[Funky]

Thanks for the suggestion! I tried it but the 4th line have a wrong syntax for the csharp compiler. But I tried to modify the line with help of your suggestion and wrote this piece of code which was ok for the compiler:

[DllImport("MXOTDLL.DLL", EntryPoint = "MXReadFingerFromSensor")]
public static extern int ReadFingerFromSensor(ref byte[,] FingerBuf);
 
byte[,] fingerBuf = new byte[256, 304];
int ret = USBFingerprintReader.ReadFingerFromSensor(ref fingerBuf);

It's ok for the compiler but my application crashes. I think that's because I couldn't give to the funtion the argument fingerBuf like this: ref fingerBuf[0, 0]. The compiler spitts out this error explanation:

Error 1 The best overloaded method match for 'Docking.PrecitajOdtis.USBFingerprintReader.ReadFi ngerFromSensor(ref byte[*,*])' has some invalid arguments D:\My docs\Visual Studio 2008\Projects\Docking\Docking\PrecitajOdtis.cs 80 14 Docking
Error 2 Argument '1': cannot convert from 'ref byte' to 'ref byte[*,*]' D:\My docs\Visual Studio 2008\Projects\Docking\Docking\PrecitajOdtis.cs 80 60 Docking


But I still do not understand, what this type means: byte[,] :). So I think I just have a syntactical problem because I don't know how to use this kind of arrays. If you would like to test the dll you also must have the device for reading finger prints :|.

Regards.

[Funky]

Uh ... I just have to change the function argument definition so it is only a byte, not an array:

[DllImport("MXOTDLL.DLL", EntryPoint = "MXReadFingerFromSensor")]
public static extern int ReadFingerFromSensor(ref byte FingerBuf);
 
byte[,] fingerBuf = new byte[256, 304];
int ret = USBFingerprintReader.ReadFingerFromSensor(ref fingerBuf[0, 0]);

Now the app doesn't crash!

I'd still like to know what byte[,] means :). I thing it is kind of 2D array.

[Plater]

If your unmanaged function def took a byte array, I am surprised it works when only getting a single byte (which would be I guess an an array of "1")
How you tested it thoroughly? Seems like there would be memory corruption if it expects to be using an X by Y 2D array but only gets the memory allocated for it of a single byte.

[balabaster]

Sorry, the change you put is correct:

byte[,] FingerBuf = new byte[256,304];

I must be spending too much time writing VB instead of C#...eek.

byte[,] initializes a 2 dimensional array of type byte. A byte is really a numeric representation of some value in the system. For instance the character "A" might really be stored as numeric value 65 (I don't recall if that's the correct value off the top of my head).

new byte[256,304] assigns a size to the byte array - think of it like a spreadsheet with 256 cells across and 304 cells wide.

Each relevant co-ordinate (represented by a corresponding "cell" of your "spreadsheet") would hold a value pertaining to what the fingerprint reader sees at that co-ordinate. The byte array is really a numeric representation of your fingerprint.

[Funky]

I suspected it is a 2D array but I didn't knew that besides array[][] definition exists also array[,] definition :) maybe it isn't quite the same thing.

Plater: I tested the code for reading a finger print and store it to a bitmap image to disc. It works well. It seems that the function needs only the first pointer of the "spreadsheet" (like balabaster said) of the fingerprint picture grid - array[0, 0] or the pointer to the first cell. The function can then get all the other cells.

Regards.