interop: Passing pointer to COM to efficiently receive large data chunk

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I'm writing COM to expose some unmanaged imagery generation functions to c#.
My question is how to best (easiest, clearest coding style) pass a managed
pointer to COM to receive back a loaded image:

example 1: using safearray
COM:
process([in,out] SAFEARRAY* bytes)
C# call:
byte[] bytes = byte[256];
process(bytes);

Question: does this pass a pointer, or is it marshalled (i.e inefficient)?


example 2: using fixed array size
COM:
process([in,out] byte[256] bytes]

Disadvantage: fixed size must be specified up front -- or is it safe to
write past the apparently "fixed" array size internal to the com function if
the true size of array is also passed as a parameter? (i.e in the case that
image size should vary fro 256?)


What it the current wisdom of how to do this best?


thanks in advance.

-Robert


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