From: James Kanze (kanze_at_[hidden])
Date: 2002-01-27 12:21:46
"Stewart, Robert" <stewart_at_[hidden]> writes:
|> From: Karl Nelson [SMTP:kenelson_at_[hidden]]
|> > > > Try deviating from the printf-like notation in the format
|> > > > string since this isn't allowing for any printf-like
|> > > > functionality:
|> > > > format(",  -th try")[40.23](hex)["toto"];
|> > This format statement is rediculously overblown. I have enough
|> > problems with overloading the modulus operator to something
|> > non-directional. making  take non-integer arguments seems
|> > totally out of place.
|> Are you familiar with std::map? It offers the subscript operator as
|> a way of accessing elements, and the keys need not be integers.
|> Consequently, there is precedence for non-integer arguments between
|> "[" and "]".
Certainly. On the other hand, when I see , I expect that the second
 applies to the results of the first. I also expect that the operator
implements something at least vaguely resembling a projection. Anything
else is blatant misuse of operator overloading, and tends to justify
Java's omitting it.
While I"m at it, I might add that when the original iostream were
developped, a lot of thought went into the choice of the operator.
(Without member templates, the option of not using an operator at all
wasn't available.) The choice of << wasn't just random. The operator
had a number of things going for it; high on the list were an acceptable
precedence (which isn't the case for %), the visual aspect, and the fact
that most programmers probably weren't really using it for anything, so
associating the meaning output to it didn't create confusion.
As it is, % simply doesn't work because of the precedence, and  leads
to confusion, as the operator is widely used, in just about every
program, for other things.
|> > Can we stick to just the format with operator <<, format with
|> > operator %, and format with variable arguments for the discussion?
|> No, but we can discuss that, too.
|> > I still think that it is not unrealistic to simply write
|> > format(cout,"%3$s, %1$s %2$s-th try") << 40.23 << hex << 50 << "toto" ;
|> > It looks like a stream and it is compact.
|> I'm not the least bit familiar with Unix98 printf() format
|> specifiers, so I don't know what that format means. (I purposely
|> skipped that part of the documentation, because printf()
|> compatibility is not important to me.) I'm going to guess that the
|> printf() % specifiers can have an embedded positional indicator
|> which is a number followed by $. Given that, and assuming that
|> format complains at compile time when %s isn't given a string as
|> shown in your example,
It shouldn't complain, but rather format whatever it is given as a
string. What that means needs some specifying, of course, but I don't
think it acceptable to refuse 0 for a "%1$f" specifier. (As for compile
time checking, of course, that simply isn't possible, because in real
code, the compiler doesn't see the format string.)
|> I still have one problem: I can't tell whether "hex" is a variable
|> in scope at this point, or whether it std::hex brought into scope
|> via some IOStreams header. That may not be a likely point of
|> confusion for "hex," but my point is that you can't tell that 50 is
|> argument 2, not 3.
Which is yet another good argument to not use manipulators.
-- James Kanze mailto:kanze_at_[hidden] Conseils en informatique orientée objet/ Beratung in objektorientierter Datenverarbeitung Ziegelhüttenweg 17a, 60598 Frankfurt, Germany Tel. +49(0)179 2607481
Boost list run by bdawes at acm.org, gregod at cs.rpi.edu, cpdaniel at pacbell.net, john at johnmaddock.co.uk