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From: Keith Thompson <kst-u@mib.org>
Newsgroups: comp.lang.c
Subject: Re: Spurious diagnostic messages
Date: Mon, 27 Jul 2015 08:19:40 -0700
Organization: None to speak of
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glen herrmannsfeldt <gah@ugcs.caltech.edu> writes:
> Bartc <bc@freeuk.com> wrote:
>> On 26/07/2015 23:35, Keith Thompson wrote:
[...]
>>>   "%b" is not currently used, so that would be the
>>> obvious solution.
>  
>> %b is supported by lccwin and by Digital Mars C (which was a surprise as 
>> it's pretty old).
>  
>>> A "#" flag could cause printf to print the "0b"
>>> or "0B" prefix; "%#b" could print a "0b" suffix, "%#B" could print a
>>> "0B" prefix, and "%b" and "%B" would be identical (unlike "%x" and
>>> "%X").
>
> Does this # flag exist for %x and %o? 

Yes. "%#x" adds a "0x" prefix, and "%#o" adds a "0" prefix if it's
not already there.

I generally don't use the "#" flag myself; I find "0x%x" clearer.  But
it's in the standard, and conforming implementations must support it.
If "%b" were added, not supporting "%#b" would be gratuitously
inconsistent.  And there's precedent for it; Perl's printf and sprintf
functions support "%b" and"%#b".

-- 
Keith Thompson (The_Other_Keith) kst-u@mib.org  <http://www.ghoti.net/~kst>
Working, but not speaking, for JetHead Development, Inc.
"We must do something.  This is something.  Therefore, we must do this."
    -- Antony Jay and Jonathan Lynn, "Yes Minister"