Talk:cpp/locale/num put/put

In the example you have:

  std::ostreambuf_iterator<CharT, Traits> it(os);
  std::use_facet<std::num_put<CharT>>(os.getloc())
         .put(it, os, os.fill(), b.x);

But in the example "std::num_put<CharT>" is wrongly using "default" ostreambuf_iterator<CharT> with "default" Traits which is a problem if the "basic_ostream<CharT, Traits>" uses some "non-default" Traits. Shouldn't it be rather ?:

  // std::ostreambuf_iterator<CharT, Traits> it(os);
  std::use_facet<std::num_put<CharT, ostreambuf_iterator<CharT, Traits>>>(os.getloc())
               .put(os, os, os.fill(), b.x);

The first arg. "os" of "put" func will be implicitly converted from "basic_ostream<CharT, Traits>" to "ostreambuf_iterator<CharT, Traits>".

Thank you.

vlakov --193.58.194.195 20:32, 21 March 2014 (PDT)

That example is already part-pseudocode (the part that sets badbit and rethrows the original exception if badbit is set is just a comment) - and you point out another reason why it's not suitable for use in a library. Personally, I am not sure it's helpful at all - I'd rather nix it and only keep the one that extends the facet (since that demonstrates why there is a do_put), or maybe move it into the [operator<< page as a "possible implementation" (which is a different section from "example") --Cubbi (talk) 17:29, 22 March 2014 (PDT)

Every example that is on en.cppreference.com is very helpful. Eliminating examples will not help too much to mortals like me. --vlakov 88.212.37.48 23:29, 22 March 2014 (PDT)

The note says `The leading zero generated by the conversion specification #o` is not counted as a padding character. But if this zero should be separated by thousands separator in Stage 2? Or undefined behaviour? with CLang prefix zero is separated while gcc doesn't.

   struct my_format : std::numpunct<char> {
       char do_thousands_sep() const override { return ','; }
       std::string do_grouping() const override { return "\3"; }
   } en_us;
   std::cout.imbue(std::locale(std::locale(), &en_us));
   std::cout << std::oct << std::showbase << 0123456 << std::endl;

what should the result be, "0123,456" or "0,123,456" ?

nice repro. This would be a good question for std-discussion --Cubbi (talk) 06:29, 2 July 2018 (PDT)