Help Marshaling a C function in C#

Question

I'm trying to call a C function from C#.
Here is the function from the C header file :

int __stdcall GetImageKN (unsigned short *ndat );

And from the documentation about this function :

ndat :
Pointer of the grayscale image data acquiring buffer.
Always secure the range image storage area using the application program.
The size of the range image data storage area should be:
160’ 120 ‘2 = 38400 bytes
The grayscales are returned as 8 bit that is doubled from 7-bit.

How do I invoke this function and read the image data ?
Thanks,
SW

Anton Tykhyy · Accepted Answer · 2011-02-08 19:11:56Z

30Kb is a small buffer. If your function runs quickly, you can rely on default marshaling behaviour and do this:

[DllImport ("your.dll")] extern int GetImageKN (short[] ndat) ; var buffer = new short[160 * 120] ; var result = GetImageKN (buffer) ;

Even if it can block for a long time, you can get away with this if you don't call this function on many threads at once.

Alex · Accepted Answer · 2011-02-08 19:05:36Z

1

[DllImport ("your.dll")] extern int GetImageKN (IntPtr ndat);

will probably do...

EDIT

generally pointers are represented as IntPtr. you can create a managed array and Marshal it to IntPtr,

edited Feb 8, 2011 at 19:05

answered Feb 8, 2011 at 18:57

Alex

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3 Comments

Vlad Over a year ago

But one should pass an address of an array to the function. How can ndat represent such an array?

Shachar Weis Over a year ago

ndat is output, how do I read the array values from an IntPtr ?

Alex Over a year ago

@Weis: it looks like ndat is parameter you are passing in, if you are expecting the function to modify it, you can decorate it with [Out] attribute and it will be modified. you can also marshal it back to managed array when you are done. go to pinvoke.net for tons of examples on how to use it.

Vlad · Accepted Answer · 2011-02-08 19:18:56Z

I would try the following:

[DllImportAttribute("your.dll", CallingConvention=CallingConvention.StdCall)] extern int GetImageKN( [Out, MarshalAs(UnmanagedType.LPArray, SizeConst=38400)] ushort[] ndat);

Not really sure however.

Davide Piras · Accepted Answer · 2011-02-08 19:00:31Z

0

ushort ndat= 123; GetImageKN(ref ndat);

answered Feb 8, 2011 at 19:00

Davide Piras

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