"Matthew Blakley" <zarcher@nospam.yahoo.com> writes:
> I'm curious as to what, if anything, was considered for providing positional
> parameters in iostreams for the Standard C++ library.

I would assume nothing. You can roll your own, though.

> For example, something like the following:
>
> using namespace std;
>     cout << form("<1> went to the <2> today.")
>             << pos(1) << "Bob"
>             << pos(2) << "store"
>             << endf;

Here's a simple version. It doesn't handle manipulators or
more than 10 parameters or errors.

class pos_ostream
{
 string fmt;
 ostream &target;
 vector<string> args;
public:
 pos_ostream(string f, ostream &o = cout) : fmt(f), target(o) { }
 template<typename T> pos_ostream &operator<<(const T &item)
 {
  ostringstream s;
  s << item;
  args.push_back(s.str());
  return *this;
 }
 ~pos_ostream()
 {
  for (int i = 0; i < fmt.size(); ++i)
  {
   if (fmt[i] == '%')
    target << args[fmt[++i] - 1];
   else
    target << fmt[i];
  }
 }
};

pos_ostream("%1 went to the %2 today.") << "Bob" << "store";
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On 17 Oct 99 10:21:41 GMT, Matthew Blakley <zarcher@nospam.yahoo.com> wrote:

>    cout << form("<1> went to the <2> today.")
>            << pos(1) << "Bob"
>            << pos(2) << "store"
>            << endf;

>Is anything of this nature being considered for future revisions of the
>standard?

This will just make extra overhead, because operator<< may now do one
of two things -- either write to the stream or fill in a positional
parameter.

What about type safety?  Must "<1>" be a string or int or what?  If
it is always a string, then use
   printf("%s went to the %s today." ,"Bob", "store")
If "<1>" can be anything, then we are back to regular old printf
with all its problems -- lack of compile time type safety, limited
to only the fundamental types, no exception safety.


Also consider writing your own manipulators

   class Went {
      public:
         Went(char const * who, char const * where) : who(who), where(where) { }
         std::ostream& friend operator<<(std::ostream&, const Went&);
      private:
         char const *const who;
         char const *const where;
   };

   std::ostream& operator<<(std::ostream& ostream, const Went& went) {
      return ostream << went.who << " to the " << went.where " << " today.";
   }

--
--------------
siemel b naran
--------------


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