Re: [PATCH] hash_readwrite_autotest: fix printf parameters

[Stephen Hemminger <stephen@networkplumber.org>]

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.