[ruby-ffi] Re: attach_function syntax when input args are pointers to contain return values

I think you're getting confused between parameter types and instances.

your attach_function call should be:

attach_function :GetMyString, [ :long, :pointer, :pointer ], :void

And you would call it like:

buffer = FFI::MemoryPointer.new(:char, 256)

size_ref = FFI::MemoryPointer.new(:int, 1)

MyGetString(x, buffer, size_ref)

# in C: int size = *size_ref

size = size_ref.read_int

string = buffer.get_string(0, size)

On Friday, February 1, 2013 6:21:44 AM UTC+10, Rob Marshall wrote:

Hi,

My guess is that this has been asked before, but I didn't find it...not exactly sure what to search for...

Anyway, I am trying to attach functions that return :void but use the input parameters to hold the return values. e.g. A function that gets a value and returns it as a string and length. So say my C-function declaration is:

void GetMyString(const long reference, char *buffer, int *size)

My guess, and I'm sure it doesn't work because I tried it, was to do:

buffer = FFI::MemoryPointer.new(:char, 256)
size = FFI::MemoryPointer.new(:int,1)
attach_function :GetMyString, [ :long, buffer, size ], :void

I got a "can't resolve type" error when I tried that.

What's the correct way to do it?

Thanks,

Rob

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