Using C++ library in C#

Question

Hi.

I need help with my code.
I'm trying to run unmanaged code from my C# code.

C++ Code
Result_t oemGetImage(PBYTE pImageBuffer,
                     PDWORD pdwSize, WORD nTop,
                     WORD nLeft, WORD nRight,
                     WORD nBottom, WORD nSkip,
                     WORD nBits, FileFormat_t nFormat,
                     WORD nWhiteValue,
                     WORD nExposeAttempts, WORD nGap,
                     BOOL Invert, void (*fpProgress) (WORD));

I don't know what to do with pImageBuffer, pdwSize or void (*fpProgress) (WORD)).

In C++ I execute this function like this:

BYTE *pBufor;
pBufor = new BYTE[MAX_IMAGE_SIZE];

DWORD *pSize;
    pSize = new DWORD;

oemGetImage (pBufor,pSize, 0, 0, 200, 200, 1, 8, FF_RAW_GRAY, 200, 100, 55, false, NULL);

FF_RAW_GRAY is an enum with value of 1.

How can I declare pBufor which is a pointer to byte array?
And what to do with void (*fpProgress) (WORD))??

Thank you, for all your help.

Vulpes · Answer

I'd declare the PBYTE parameter in C# like this: [In Out]byte[] pImageBuffer and pass it Bufor where: byte[] Bufor = new BYTE[MAX_IMAGE_SIZE]; This should work as an array variable in C# is already a pointer because arrays are reference types. The PDWORD parameter is a pointer to a DWORD so I'd declare that as: ref uint pdwSize and then pass it pSize where: uint pSize = 0; The final parameter is of course a function pointer. The equivalent in C# would be a delegate of the appropriate type: [UnmanagedFunctionPointer(CallingConvenction.Cdecl)] // if it is Cdecl public delegate void Progress (ushort us); so you could declare it as [MarshalAs(UnmanagedType.FunctionPtr)]Progress fpProgress and pass it null.

Vulpes · Answer

Pleased to hear that you've got it working now :) The attribute you mention would only have been needed if the C++ function was using the Cdecl calling convention rather than the default Winapi (or StdCall) calling convention which evidently it was not.

Peter · Answer

Thank you Vulpes for yor help. Your solution worked perfectly! However [UnmanagedFunctionPointer(CallingConvenction.Cdecl)] can't be resolved in my solution. Luckily everything worked fine without this line. My definition for this function looks like this: private extern static int oemGetImage([In Out]byte[] pImageBuffer ref uint pdwSize uint nTop uint nLeft uint nRight uint nBottom uint nSkip uint nBits uint nFormat uint nWhiteValue uint nExposeAttempts uint nGap bool Invert [MarshalAs(UnmanagedType.FunctionPtr)]Progress fpProgress); public delegate void Progress(ushort us); and execution byte[] pBufor = new byte[width * height]; uint pSize = 0; oemGetImage(pBufor ref pSize 0 0 _width _height 1 8 1 220 50 35 false null); Thank you so much!