Re: PRI* considered harmful

From	Keith Thompson <kst-u@mib.org>
Newsgroups	comp.std.c
Subject	Re: PRI* considered harmful
Date	2011-07-07 16:46 -0700
Organization	None to speak of
Message-ID	<lnhb6xzmbf.fsf@nuthaus.mib.org> (permalink)
References	<87mxgqhk3x.fsf@once.weird.com> <iv427t$ed2$1@dont-email.me> <8762ndhnfs.fsf@once.weird.com> <lntyaxztes.fsf@nuthaus.mib.org> <87oc15g10i.fsf@once.weird.com>

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"Greg A. Woods" <woods@robohack.org> writes:
> Keith Thompson <kst-u@mib.org> writes:
>> (I suppose PRI32d could be defined as "ld" even if int32_t is a typedef
>> for int, but only if "%ld" actually works with an int32_t or int
>> argument.)
>
> Exactly, and thus a compiler that cares about portability must then
> complain that format of "%ld" does not match type of "int", and
> rightfully so.

Compilers are never required to complain about printf formats.

On the other hand, compilers are *allowed* to warn about anything
they like.

Presumably an implementation that warns about mismatched printf
formats, even those that happen to work (say, because int and long
are the same size) would define the PRI* macros so they avoid those
warnings when used correctly.  For that matter, there's no good
reason for an implementation *not* to use matching definitions for
the PRI* macros; if int32_t is typedef'ed as int, then PRId32 will
probably be defined as "d", even if "ld" would also work.

I suggest that, at least in this specific case, you're looking for
problems that are unlikely to exist in any real implementation.

> You can't escape the casts with the PRI* macros even if you're just
> trying to play with ints and longs.

If you're printing ints and longs, you don't need to use the PRI*
macros.  Just use "%d" and "%ld", respectively.  Or did I misunderstand
your point?

> (Maybe the standard should be fixed in this respect, but it wouldn't
> really solve enough of the problems with the PRI* debacle.)
>
>
>> The language and library don't make it *easy* to print raw time_t
>> values because there's rarely a good reason to do so.  That's what
>> strftime() is for.
>
> It might be rare in your world, but it's far from rare in my world.
>
> Also, I repeat, C99 strftime() is unable to print the value of a time_t
> as an integer representation of seconds since the epoch of time_t.  (C99
> does not have the '%s' specifier that many implementations do have.)

That's because the language doesn't say that time_t represents an
integer number of seconds since some epoch.  It says only that it's
an arithmetic type "capable of representing times".  Among many
other possibilities, it could use the value 20110707233829, or
0x20110707233829, or 020110707233829, to represent the current time.
Or the resolution could be larger or smaller than one second.
The relationship between time_t values and real times needn't even
be linear.

No, the PRI* macros do not solve the problem of printing raw time_t
values; they're not intended to.  I do sometimes print such values
myself; I generally just write something like

    printf("%ld\n", (long)time(NULL));

which isn't entirely portable, but it's good enough for most purposes.

>> The only library-defined *integer* type that isn't covered, as far
>> as I can tell, is wchar_t.  You wouldn't normally want to print that
>> as integer value anyway.
>
> It's not the only one (not even close).

So what are the others?

> Never assume what's "normal", especially not when designing a standard.

Don't assume that the PRI* macros are intended to solve the problem
of printing values of any and all language-defined integer types.
They're not.  Since it's straightforward to print any integer value
by converting it to intmax_t or uintmax_t, I don't see that this
is much of a problem.

Personally, I don't think I've ever used the PRI* macros.  I prefer
to convert to intmax_t or uintmax_t, or to long or unsigned long if
I'm using a non-C99 implementation or if I'm printing a type that
I happen to know is no wider than long.  That doesn't mean I don't
thing the PRI* macros should exist; there are plenty of language
and library features I don't use myself.

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Nokia
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"

Thread

PRI* considered harmful "Greg A. Woods" <woods@robohack.org> - 2011-07-06 19:58 -0700
  Re: PRI* considered harmful William Ahern <william@wilbur.25thandClement.com> - 2011-07-06 20:38 -0700
    Re: PRI* considered harmful "Greg A. Woods" <woods@robohack.org> - 2011-07-06 22:26 -0700
      Re: PRI* considered harmful Jens Gustedt <Jens.Gustedt@loria.fr> - 2011-07-07 08:52 +0200
        Re: PRI* considered harmful "Greg A. Woods" <woods@robohack.org> - 2011-07-07 14:11 -0700
          Re: PRI* considered harmful Jens Gustedt <Jens.Gustedt@loria.fr> - 2011-07-08 11:58 +0200
        Re: PRI* considered harmful lawrence.jones@siemens.com - 2011-07-07 17:58 -0400
          Re: PRI* considered harmful Jens Gustedt <Jens.Gustedt@loria.fr> - 2011-07-08 12:02 +0200
      Re: PRI* considered harmful lawrence.jones@siemens.com - 2011-07-07 17:57 -0400
        Re: PRI* considered harmful Keith Thompson <kst-u@mib.org> - 2011-07-07 15:42 -0700
          Re: PRI* considered harmful lawrence.jones@siemens.com - 2011-07-08 08:56 -0400
  Re: PRI* considered harmful James Kuyper <jameskuyper@verizon.net> - 2011-07-07 06:36 -0400
    Re: PRI* considered harmful "Greg A. Woods" <woods@robohack.org> - 2011-07-07 12:59 -0700
      Re: PRI* considered harmful Keith Thompson <kst-u@mib.org> - 2011-07-07 14:12 -0700
        Re: PRI* considered harmful "Greg A. Woods" <woods@robohack.org> - 2011-07-07 15:49 -0700
          Re: PRI* considered harmful Keith Thompson <kst-u@mib.org> - 2011-07-07 16:46 -0700
            Re: PRI* considered harmful "Greg A. Woods" <woods@robohack.org> - 2011-07-07 18:26 -0700
              Re: PRI* considered harmful James Kuyper <jameskuyper@verizon.net> - 2011-07-07 22:35 -0400
                Re: PRI* considered harmful "Greg A. Woods" <woods@robohack.org> - 2011-07-07 20:58 -0700
                Re: PRI* considered harmful Wojtek Lerch <wojtek_l@yahoo.ca> - 2011-07-08 00:28 -0400
                Re: PRI* considered harmful James Kuyper <jameskuyper@verizon.net> - 2011-07-08 07:41 -0400
                Re: PRI* considered harmful "Greg A. Woods" <woods@robohack.org> - 2011-07-08 23:05 -0700
                Re: PRI* considered harmful Keith Thompson <kst-u@mib.org> - 2011-07-09 00:50 -0700
                Re: [incorrectly implementd] PRI* considered harmful James Kuyper <jameskuyper@verizon.net> - 2011-07-09 06:38 -0400
                Re: PRI* considered harmful Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2011-07-09 21:07 +0200
                Re: PRI* considered harmful Keith Thompson <kst-u@mib.org> - 2011-07-08 09:52 -0700
              Re: PRI* considered harmful Richard Kettlewell <rjk@greenend.org.uk> - 2011-07-08 11:45 +0100
                Re: PRI* considered harmful "Greg A. Woods" <woods@robohack.org> - 2011-07-08 23:14 -0700
                Re: PRI* considered harmful Keith Thompson <kst-u@mib.org> - 2011-07-09 00:47 -0700
                Re: PRI* considered harmful Richard Kettlewell <rjk@greenend.org.uk> - 2011-07-09 10:51 +0100
                Re: PRI* considered harmful James Kuyper <jameskuyper@verizon.net> - 2011-07-09 06:43 -0400
              Re: PRI* considered harmful Keith Thompson <kst-u@mib.org> - 2011-07-08 09:49 -0700
                Re: PRI* considered harmful "Greg A. Woods" <woods@robohack.org> - 2011-07-08 23:24 -0700
                Re: PRI* considered harmful Keith Thompson <kst-u@mib.org> - 2011-07-09 00:45 -0700
                Re: PRI* considered harmful "Greg A. Woods" <woods@robohack.org> - 2011-07-09 16:18 -0700
                Re: PRI* considered harmful Keith Thompson <kst-u@mib.org> - 2011-07-09 18:57 -0700
                Re: PRI* considered harmful Keith Thompson <kst-u@mib.org> - 2011-07-13 09:37 -0700
                Re: PRI* considered harmful James Kuyper <jameskuyper@verizon.net> - 2011-07-09 06:46 -0400
                Re: PRI* considered harmful Harald van Dĳk <truedfx@gmail.com> - 2011-07-09 08:09 -0700
                Re: PRI* considered harmful Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2011-07-11 16:00 +0300
                Re: PRI* considered harmful Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2011-07-09 20:59 +0200
                Re: PRI* considered harmful Keith Thompson <kst-u@mib.org> - 2011-07-09 12:22 -0700
                Re: PRI* considered harmful Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2011-07-09 21:32 +0200
                Re: PRI* considered harmful Keith Thompson <kst-u@mib.org> - 2011-07-09 12:54 -0700
                Re: PRI* considered harmful Marcin Grzegorczyk <mgrzegor@poczta.onet.pl> - 2011-07-09 23:39 +0200
                Re: PRI* considered harmful "Greg A. Woods" <woods@robohack.org> - 2011-07-09 16:56 -0700
                Re: PRI* considered harmful "Greg A. Woods" <woods@robohack.org> - 2011-07-09 16:52 -0700
                Re: PRI* considered harmful Keith Thompson <kst-u@mib.org> - 2011-07-09 18:53 -0700
                Re: PRI* considered harmful Jens Gustedt <Jens.Gustedt@loria.fr> - 2011-07-10 14:12 +0200
                Re: PRI* considered harmful Marcin Grzegorczyk <mgrzegor@poczta.onet.pl> - 2011-07-11 20:22 +0200
                Re: PRI* considered harmful Jens Gustedt <Jens.Gustedt@loria.fr> - 2011-07-10 13:57 +0200
                Re: PRI* considered harmful "Greg A. Woods" <woods@robohack.org> - 2011-07-09 16:49 -0700
                Re: PRI* considered harmful Jens Schweikhardt <usenet@schweikhardt.net> - 2011-07-19 19:28 +0000
      Re: PRI* considered harmful Tim Rentsch <txr@alumni.caltech.edu> - 2011-07-07 14:13 -0700
  Re: PRI* considered harmful Keith Thompson <kst-u@mib.org> - 2011-07-09 01:04 -0700
    Re: PRI* considered harmful "Greg A. Woods" <woods@robohack.org> - 2011-07-09 17:23 -0700
      Re: PRI* considered harmful Keith Thompson <kst-u@mib.org> - 2011-07-09 19:03 -0700
        Re: PRI* considered harmful Marcin Grzegorczyk <mgrzegor@poczta.onet.pl> - 2011-07-11 20:40 +0200
          Re: PRI* considered harmful Keith Thompson <kst-u@mib.org> - 2011-07-11 11:56 -0700
            Re: PRI* considered harmful Marcin Grzegorczyk <mgrzegor@poczta.onet.pl> - 2011-07-11 21:40 +0200
              Re: PRI* considered harmful Keith Thompson <kst-u@mib.org> - 2011-07-11 13:16 -0700
                Re: PRI* considered harmful Marcin Grzegorczyk <mgrzegor@poczta.onet.pl> - 2011-07-11 23:29 +0200
                Re: PRI* considered harmful Keith Thompson <kst-u@mib.org> - 2011-07-11 14:46 -0700
              Re: PRI* considered harmful "Greg A. Woods" <woods@robohack.org> - 2011-07-12 22:18 -0700
                Re: PRI* considered harmful Keith Thompson <kst-u@mib.org> - 2011-07-13 09:00 -0700
  Re: PRI* considered harmful Richard Kettlewell <rjk@greenend.org.uk> - 2011-07-09 20:30 +0100

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