Re: sig2str and str2sig use in C++

[Daniel J Sebald]

On 06/10/2013 09:36 PM, Daniel J Sebald wrote:
> On 06/10/2013 05:47 PM, Paul Eggert wrote:
> > On 06/05/13 09:57, Daniel J Sebald wrote:
> > > Well, taking this all into consideration, perhaps the easiest thing
> > > to do is construct a table at runtime on the heap:
> >
> > I'd rather avoid the runtime overhead.
> >
> > How about something like this?
> >
> > enum { HUP_OFFSET = 0 };
> > #define HUP_STRING "string for SIGHUP"
> >
> > enum { INT_OFFSET = HUP_OFFSET + sizeof HUP_STRING };
> > #define INT_STRING "string for SIGINT"
> >
> > enum { QUIT_OFFSET = INT_OFFSET + sizeof INT_STRING };
> > #define QUIT_STRING "string for SIGQUIT"
> >
> > A bit awkward, but no repeated strings; and I've seen worse.
>
> Yes, something like that would work. Keep in mind that there needs to be
> a conditional. So might it be something like:
>
> enum { HUP_OFFSET = 0 };
> #ifdef SIGHUP
> #define HUP_STRING "string for SIGHUP"
> #else
> #define HUP_STRING ""
> #endif
>
> enum { INT_OFFSET = HUP_OFFSET + sizeof HUP_STRING };
> #ifdef SIGINT
> #define INT_STRING "string for SIGINT"
> #else
> #define INT_STRING ""
> #endif
>
> enum { QUIT_OFFSET = INT_OFFSET + sizeof INT_STRING };
> #ifdef SIGQUIT
> #define QUIT_STRING "string for SIGQUIT"
> #else
> #define QUIT_STRING ""
> #endif
>
> etc. Otherwise one would have to condition the definitions inside the
> enum with what is actually defined, i.e.,
>
> enum { QUIT_OFFSET = ?????? + sizeof ?????? }
>
> which would get awkward. But actually maybe these definitions could all
> be left unconditioned because if they appear in this big character
> string somewhere it is really only the pointer (i.e., offset) that matters.
>
> But then what about indexing that array? One would still need to assign
> the values of the definitions somehow, and the goal is to somehow group
> the signal synonyms, so maybe something like:
>
> #define END_OF_STRINGS '\0',
>
> char sig_strings[] = {
> #ifdef SIGHUP
> HUP_STRING, '\0',
> END_OF_STRINGS
> #endif
>
> #ifdef SIGINT
> INT_STRING, '\0',
> END_OF_STRINGS
> #endif
>
> #ifdef SIGQUIT
> QUIT_STRING, '\0',
> END_OF_STRINGS
> #endif
>
> ...
>
> #ifdef SIGCHLD
> CHLD_STRING, '\0',
> #ifndef SIGCLD
> END_OF_STRINGS
> #endif
> #endif
>
> #ifdef SIGCLD
> CHD_STRING, '\0',
> END_OF_STRINGS
> #endif
>
> etc.
> }
>
> #define NUMOFFSET(name) { SIG##name, #name }
>
> /* Signal names and numbers. Put the preferred name first. */
> static struct numname { int num; int offset; } numoffset_table[] =
> {
> /* Signals required by POSIX 1003.1-2001 base, listed in
> traditional numeric order where possible. */
> #ifdef SIGHUP
> NUMOFFSET (HUP),
> #endif
> #ifdef SIGINT
> NUMOFFSET (INT),
> #endif
> #ifdef SIGQUIT
> NUMOFFSET (QUIT),
> #endif
> ...
> #ifdef SIGCHLD
> NUMOFFSET (CHLD),
> #else
> #ifdef SIGCLD
> NUMOFFSET (CLD),
> #endif
> #endif
> etc.
> };
>
> Notice how there is only one possible pointer for a number. But there
> too it might not make a difference if there is more than one because the
> algorithm will just pick the first entry it finds and if NUMOFFSET
> (CHLD) and NUMOFFSET (CLD) produce the same character offset, no problem.
>
> It seems there are a number of variations to defining the array that
> will work, but the important point is the character string definition:
>
> CHLD_STRING, '\0',
> #ifdef SIGCLD
> CHD_STRING, '\0',
> #endif
> END_OF_STRINGS

I may have lost the train of thought on this.  Were we thinking that 
character array would contain one or two null terminated strings and 
then an empty string (what I described) so that some routine could 
return a pointer to just the strings associated with that number, e.g.,

char *sig2str2 ();

Or were we thinking to have a list of all the strings that are defined 
so that the user can then use str2sig () to get the numbers like I did 
in my second example from a few posts back?  In the latter case it would be:

#define END_OF_STRINGS '\0',

char sig_strings[] = {
#ifdef SIGHUP
  HUP_STRING, '\0',
#endif
#ifdef SIGINT
  INT_STRING, '\0',
#endif
#ifdef SIGQUIT
  QUIT_STRING, '\0',
#endif
...
#ifdef SIGCHLD
  CHLD_STRING, '\0',
#endif
...
#ifdef SIGCLD
  CLD_STRING, '\0',
#endif
...
  END_OF_STRINGS
};

That's somewhat more straightforward.

Dan