[9fans] why does this compile?

[9fans] why does this compile?

[erik quanstrom]

this is rejected by most other compilers because
rlogn is not initialized to a constant.  the value
returned is bizarre.

- erik

> #include <u.h>
> #include <libc.h>
>
> static char  rlog[24];
> static char *rloge = rlog + sizeof rlog;
> static char *rlogl = rlog + sizeof rlog - 1;
> static char *rlogn = rloge - 1;
>
> void
> main(int, char **)
> {
> 	print("%p %p %p %p\n", rlog, rlogl, rlogn, rloge);
> 	exits(nil);
> }

Re: [9fans] why does this compile?

[Charles Forsyth]

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On 14 February 2013 21:15, erik quanstrom <quanstro@quanstro.net> wrote:

>  the value
> returned is bizarre.
>

it's the (lvalue of rloge)-1, not bizarre.

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Re: [9fans] why does this compile?

[erik quanstrom]

On Thu Feb 14 16:23:21 EST 2013, charles.forsyth@gmail.com wrote:

> On 14 February 2013 21:15, erik quanstrom <quanstro@quanstro.net> wrote:
>
> >  the value
> > returned is bizarre.
> >
>
> it's the (lvalue of rloge)-1, not bizarre.

is that a legal thing to do?

- erik

Re: [9fans] why does this compile?

[Charles Forsyth]

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No, but the value at least isn't bizarre. It would be correct for rloge as
an array, and i assume it gets through because of the way the
array->pointer change is done. Even so, if it had been GCC, by now it would
be an essential extension, and have been used to implement an elisp
interpreter, shave micro cycles from the time of a Java vm , and by GCC
itself. I might look at nipping all that in the bud tomorrow, although I
think I have looked at this once before.
On 14 Feb 2013 21:27, "erik quanstrom" <quanstro@quanstro.net> wrote:

> On Thu Feb 14 16:23:21 EST 2013, charles.forsyth@gmail.com wrote:
>
> > On 14 February 2013 21:15, erik quanstrom <quanstro@quanstro.net> wrote:
> >
> > >  the value
> > > returned is bizarre.
> > >
> >
> > it's the (lvalue of rloge)-1, not bizarre.
>
> is that a legal thing to do?
>
> - erik
>
>

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Re: [9fans] why does this compile?

[erik quanstrom]

On Thu Feb 14 16:49:17 EST 2013, charles.forsyth@gmail.com wrote:

> No, but the value at least isn't bizarre. It would be correct for rloge as
> an array, and i assume it gets through because of the way the
> array->pointer change is done. Even so, if it had been GCC, by now it would
> be an essential extension, and have been used to implement an elisp
> interpreter, shave micro cycles from the time of a Java vm , and by GCC
> itself. I might look at nipping all that in the bud tomorrow, although I
> think I have looked at this once before.

thanks.

- erik