On 03/19/2014 02:30 AM, Bruce Momjian wrote:
On Tue, Mar 18, 2014 at 09:13:28PM +0200, Heikki Linnakangas wrote:
On 03/18/2014 09:04 PM, Simon Riggs wrote:
On 18 March 2014 18:55, Alvaro Herrera <alvhe...@2ndquadrant.com> wrote:

That said, I don't find comma expression to be particularly "not

Maybe, but we've not used it before anywhere in Postgres, so I don't
see a reason to start now. Especially since C is not the native
language of many people these days and people just won't understand

Agreed. The psqlODBC code is littered with comma expressions, and
the first time I saw it, it took me a really long time to figure out
what "if (foo = malloc(...), foo) { } " meant. And I consider myself
quite experienced with C.

I can see how the comma syntax would be confusing, though it does the
job well.  Attached is a patch that does the double-errno.  However,
some of these loops are large, and there are 'continue' calls in there,
causing the addition of many new errno locations.  I am not totally
comfortable that this new coding layout will stay unbroken.

Would people accept?

        for (errno = 0; (dirent = readdir(dir)) != NULL; errno = 0)

That would keep the errno's together and avoid the 'continue' additions.

That's clever. A less clever way would be:

for (;;)
  errno = 0;
  if ((dirent = readdir(dir)) != NULL)


I'm fine with either, but that's how I would naturally write it.

Yet another way would be to have a wrapper function for readdir that resets errno, and just replace the current readdir() calls with that.

And now that I look at initdb.c, walkdir is using the comma expression for this already. So there's some precedence, and it doesn't actually look that bad. So I withdraw my objection for that approach; I'm fine with any of the discussed alternatives, really.

- Heikki

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