Re: curses_trace() - version 6.6

Thomas Dickey <[email protected]> Sat, 15 Aug 2026 14:35:43 -0400
Newsgroups	gmane.comp.lib.ncurses.bugs
Message-ID	<[email protected]>
On Sat, Aug 15, 2026 at 11:52:09AM -0500, G. Branden Robinson wrote:
> At 2026-08-05T15:09:13-0400, Thomas Dickey wrote:
> > On Wed, Aug 05, 2026 at 07:41:24PM +0200, Björn Försterling wrote:
> > > And `curses_trace(TRACE_MAXIMUM)` seems to return 0 even when
> > > tracing is available and writing to a file called "trace" works.
> > > Probably because the previous bitmask was 0.
> > 
> > yes :-)
> > 
> > > But how do you check if tracing is available?
> > 
> > call the function twice:
> > 
> > 	curses_trace(TRACE_MAXIMUM);
> > 	rc = trace(TRACE_NORMAL);
> > 
> > curs_set and umask do something like that with return-codes.
> 
> Ah, but you don't have to call curs_set twice.
> 
> kernel(3NCURSES)              Library calls             kernel(3NCURSES)
> ...
>      int curs_set(int visibility);
> ...
>    curs_set
>      curs_set adjusts the cursor visibility to “invisible”, “visible”,
>      “very visible”, as its argument is 0, 1, or 2, respectively.  It
>      returns the previous visibility if the requested one is supported,
>      and ERR otherwise.
> 
> curs_set returns a _signed_ integral value, with negative values
> reserved as an error indication.
> 
> Since ncurses ABI 7 appears to be open for business,[1] I propose that
> curses_trace() change its return type to a "regular" signed `int`; that
> way this pattern of calling curses_trace() twice to decide whether the
> feature is enabled becomes unnecessary.

The standards committees get that without changing the signature:

	unsigned rc = curses_trace(TRACE_NORMAL);
	if ((int)rc == ERR)
		whatever();
> 
> If the tracing feature is disabled, curses_trace() can return ERR.
> 
> There are only 13 distinct event types.
> 
> $ sed -n 209,210p include/curses.tail
> #define TRACE_SHIFT     13      /* number of bits in the trace masks */
> #define TRACE_MAXIMUM   ((1 << TRACE_SHIFT) - 1) /* maximum trace level */
> 
> Even with a PDP-11 sized `int`, you could convert `result` to `int` and
> have 2 bits to spare.  On a 32-bit machine I don't think you'll ever run
> out of room, to say nothing of 64-bit hosts.
> 
> What do you think?
> 
> Regards,
> Branden
> 
> [1] https://lists.gnu.org/archive/html/bug-ncurses/2025-05/msg00015.html
> 
> [2] It's not a "mask", but rather a bit vector; each set bit _enables_ a
>     feature rather than disabling it or "masking it off".  Early Unix
>     hackers were apparently so fascinated by the operation of umask(2)
>     and bitwise arithmetic that they extrapolated any collection of bits
>     with orthogonal meaning as a "mask".  I've been slowly cleaning the
>     same abuse of terminology out of groff's code and documentation.



-- 
Thomas E. Dickey <[email protected]>
https://invisible-island.net
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