Hello,
I wanted to share some doubts I have with the hope of them being solved.

In writing tilde externals, I've seen that in and out buffer address (in the case of a 1inlet/1outlet external) are the same. I thought it was a problem of my initialization code, but then I checked on other externals and I have seen that this always happens... I can't understand how two buffers share the same starting memory address. I expected a ping-pong strategy, with 2 pointers and two allocated memory areas, with the pointers changing from location 1 to 2 to 1 and so forth.

I digged into these details because the external I am writing crashes with a segmentation fault when I try to write to the out buffer.

while (n--)
    {
        for (i = 0; i < x->x_noutlets; i++)
        {
            *(out[i]++) = 0.;
        }
    }
This does not happen at first but after some few iterations of the perform routine. I suppose that this is due to a write in a forbidden memory area... Any suggestions?

L[/i]

For your first question, this is a common technique to save space in memory. Once you've used the input buffer, you don't need it anymore. So there's nothing wrong with just using the same space for the output buffer. I think Pd tries to be smart about this, so if there is a situation where the input and output buffers need to be different, Pd will take care of that for you. Just make sure you read from the buffer before writing to it to avoid problems.

As for the second one, I *think* the problem might be the parentheses. It might be causing the pointer to increment first before writing, so when you get to the end it's attempting to write to a memory space that's not part of the buffer. I wrote an external that essentially does what you have if the table it's trying to read from is invalid, and I omitted the parentheses. It works fine for me, so maybe give that a try.

Thanks for the explanation.

As to the bug: for some reason the while(n--) would start with values < 0 and thus would eventually touch a forbidden memory area.

That's weird. Did you find out why that was happening?

Yep, n was handled by another piece of code on top of the one I posted. So, to clarify, it does not have anything to do with Pd but with my code

L