Using C++ library in C#

Peter

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.

3 Replies

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Vulpes14y ago
Accepted 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.
Vulpes14y ago
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.
Peter14y ago
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!