Hello everybody,

We are evaluating the use of C# and GDI+ to develop a GUI based
application which elaborate image (stored as array of native type).
This application needs to call several native C functions in order to
perform some intensive computation on the image. Basically I will store
the image into array of native type (such as byte, int or double) in C#
code, than I will call the native C function passing the array. The C
function could:

- modify the array of data, do not return anything
- create a new array and return it, using the passed array data

Do this have a performance overhead? Do the arrays need to be copied
while they are passed and/or returned?

TIA
JocK

Hello there JocK. I've been grappling with same question actually, and found
out that one can pass in the whole array, when the C function is really
expecting a whole array and not just a pointer, or pass in a pointer when
it's expecting that. I've copied and pasted the transcript of corresponding
with James, below;

-----------------------
Hi James. I found out in the meantime that for the particular example where
the myFunc in the dll is expecting a real array ("data[]") and not a pointer
to one, I can pass in the array name itself, rather than a pointer to it.
With a simple test function compiled into the dll, which has a declaration in
the C# program of

[DllImport("process.dll")]
public extern static int test(int [] int_in_out);

and then with a C# array like

int [] myInt = new int[4];

after filling up the array with four integers, I can pass it in like

int result = test(myInt);

so I think the entire array is being passed in, copied in rather than just a
pointer being passed. I tried changing the "test" function so it expected a
pointer, and found that your method does indeed work. Thanks.
John

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Hope that answers your question.
John




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