RE: [PATCH] hash_readwrite_autotest: fix printf parameters

["Morten Brørup" <mb@smartsharesystems.com>]

> From: Andre Muezerie [mailto:andremue@linux.microsoft.com]
> Sent: Tuesday, 11 March 2025 15.40
> 
> On Mon, Mar 10, 2025 at 08:36:40AM -0700, Stephen Hemminger wrote:
> > On Mon, 10 Mar 2025 10:51:51 +0000
> > Bruce Richardson <bruce.richardson@intel.com> wrote:
> >
> > > On Fri, Mar 07, 2025 at 02:34:01PM -0800, Andre Muezerie wrote:
> > > > On Fri, Mar 07, 2025 at 09:01:28AM +0000, Bruce Richardson wrote:
> > > > > On Thu, Mar 06, 2025 at 12:03:28PM -0800, Andre Muezerie wrote:
> > > > > > Compiling with MSVC logs the warnings below, which result in
> > > > > > build error:
> > > > > >
> > > > > > ../app/test/test_hash_readwrite.c(73): warning C4476:
> 'printf' :
> > > > > >     unknown type field character ''' in format specifier
> > > > > > ../app/test/test_hash_readwrite.c(75): warning C4474:
> 'printf' :
> > > > > >     too many arguments passed for format string
> > > > > > ../app/test/test_hash_readwrite.c(75): note: placeholders and
> > > > > >     their parameters expect 2 variadic arguments, but 4 were
> provided
> > > > > >
> > > > > > Signed-off-by: Andre Muezerie <andremue@linux.microsoft.com>
> > > > > > ---
> > > > > >  app/test/test_hash_readwrite.c | 2 +-
> > > > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > > > >
> > > > > IF the "'" character is not supported, is there some other
> method to do
> > > > > thousands grouping in MSVC?
> > > > >
> > > > > /Bruce
> > > >
> > > > The problem exists with all compilers I tried on Windows:
> > > >
> > > > 1) MSVC logs the error I mentioned above
> > > >
> > > > 2) GCC and Clang don't complain at compile time, but don't honor
> the "'" as a special
> > > > character. As an example,
> > > > printf("%'d\n", 1024);
> > > > results in
> > > > 'd
> > > >
> > > > It seems that for this syntax to work as you would expect,
> support needs to exist in both the
> > > > compiler and the libraries used.
> > > >
> > > > Back to your question: there's no equivalent syntax on Windows
> that provides the thousands grouping.
> > > > If really needed (and I understand it is useful for large
> numbers), we could get the same result
> > > > by calling a helper function that would convert the number in the
> formatted string and use that
> > > > in the printf statement.
> > > >
> > > > There is a Win32 API that does that. It takes a string as input
> though: GetNumberFormatA.
> > > > (https://learn.microsoft.com/en-us/windows/win32/api/winnls/nf-
> winnls-getnumberformata)
> > > >
> > > > We could use ifdefs to keep the old logic on Linux and use new
> logic on Windows (for all compilers).
> > > >
> > > > Let me know if this is something that would need to be done, or
> if the current output
> > > > without thousands grouping is good enough.
> > > > --
> > > The thousands grouping is incredibly helpful when working with
> large
> > > numbers, but given the lack of support for this on Windows, we'll
> just have
> > > to go without, I think.
> > >
> > > /Bruce
> >
> > Maybe some variation of the pretty printing code that iproute2 has
> > (see print_num) would be useful. Feel free to reuse it.
> > I wrote the initial version.
> 
> That's an interesting suggestion. I'll use that.

Often "123 M" is better than "123123123", but sometimes seeing the last digit move is important, e.g. when looking at packet counters.

Just mentioning, so you consider which format is better every time you use it.