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| From | Keith Thompson <kst-u@mib.org> |
|---|---|
| Newsgroups | comp.std.c |
| Subject | Re: PRI* considered harmful |
| Date | 2011-07-11 13:16 -0700 |
| Organization | None to speak of |
| Message-ID | <lnliw4vaic.fsf@nuthaus.mib.org> (permalink) |
| References | (2 earlier) <874o2vc7ab.fsf@once.weird.com> <lnhb6ux57t.fsf@nuthaus.mib.org> <ivfg2r$ej7$1@dont-email.me> <lnpqlgve7z.fsf@nuthaus.mib.org> <ivfjj2$74j$1@dont-email.me> |
Marcin Grzegorczyk <mgrzegor@poczta.onet.pl> writes:
> Keith Thompson wrote:
>> Marcin Grzegorczyk<mgrzegor@poczta.onet.pl> writes:
> [...]
>>> That's why I'd rather propose, instead of size, an enumeration with
>>> distinct (implementation-defined) values for each valid type supported
>>> by the implementation. A standardized macro could then map expression
>>> type to an enumeration constant via the C1X generic selection construct
>>> (i.e. no compiler magic needed); as an added benefit, the macro would
>>> catch cases when a completely wrong type, like a floating-point or
>>> structure type, is passed to a specifier that expects only integer types.
>>
>> But that wouldn't handle user-defined integer types, something that
>> Greg's original proposal was *intended* to do.
>
> What user-defined types wouldn't it handle? Typedefs are just aliases
> for existing types.
The point is that you don't know *which* existing type a given type is
an alias for.
Suppose a library defines a typedef "foo_t" in a header <foo.h>.
You know it's a signed integer type, and you can determine that
it's 32 bits, which could match either int or long on your system.
If you want to print a foo_t value without converting it, do you use
"%d" or "%ld"? (If the library author was kind enough to provide a
PRIFOOd macro, you can use that, but I don't know of any libraries
that do that.)
Of course you can always cast to intmax_t and use "%jd", but then
you don't really need any of the PRI* macros.
>> I'm not sure I see the benefit of the enumeration. It seems like
>> just another set of semi-arbitrary names associated with each
>> integer type.
>
> Yes, hence the standard would not need to list those names, just define
> a macro to map, in an implementation-defined manner, types to values
> expected by *printf(). In fact, you're right that enumeration is not
> necessary; a plain int would suffice.
I don't see how such a macro would work (unless it uses compiler magic,
but in that case it isn't really a macro). Or am I missing something?
> [...]
>> but if I were designing C from scratch, I'd want to have a mechanism
>> for determining all these things from the type name itself (and it
>> could also be applied to an expression of the type).
>>
>> Ada, for example, has something called "attributes", whose syntax
>> is a prefix, followed by an apostrophe, followed by a predefined
>> attribute name. The maximum values of types Character, Integer, and
>> Float are Character'Last, Integer'Last, and Float'Last, respectively.
>
> D has something similar called properties, with a much more C-like syntax:
>
> int foo;
> long bar;
> /* ... */
> if (bar > foo.max) /* ... */
>
> But then, D actually is intended to be C designed from scratch :-)
That could work. Of course you'd have to avoid collisions between
property names and struct/union member names. Are the property
names reserved? It could be confusing for "foo.max" to mean the
maximum value of foo's type (when foo is an integer expression)
and the "max" member (when foo is a struct expression).
Personally, I'd prefer to see a unique new syntax, but C makes such
heavy use of punctuation it's hard to come up with one that doesn't
break existing code. "foo$max" might work, except that '$' in
identifiers is a common extension on VMS.
--
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"
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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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