C++ Tips: IO - form() equivalents using stream manipulators

[ben2ong2]

(Newsgroups: comp.lang.c++, 9 Dec 97)


BONAKDARIAN: Esmail Bonakdarian

> > Every printf specifier has a corresponding set of ostream specifiers.
> > They're not as compact as in C format strings, but as far as I know
> > they're as comprehensive. The Draft Standard contains a table telling
> > you which iostream specifiers correspond to which C format specifiers.

BECKER: Pete Becker <petebecker@acm.org>

Whoops, I thought there was a table, but it's not there. Bummer.

BONAKDARIAN:

> It's too bad they aren't part of the standard, esp for the basic built
> in types this would be just great. That's all I use them for anyway.
>
> Is there an easy way/wrapper function to format output in C++?
>
> For example if I had this:
>
>       int    i = 12;
>       float  f = 3.14;
>       char   str[20]; // initialized with some string
>
>       cout << form("%3d %03d  %f5.2f  %10s\n", i, i, f, str);

BECKER:

cout << setw(3) << i << ' '
     << setfill('0') << setw(3) << i << setfill(' ') << "  "
     << fixed << setw(5) << setprecision(2) << f << "    "
     << setw(10) << str;

BONAKDARIAN:

>       cout << form("%7d  %f0.2f  %-10s\n", i, f, str);

BECKER:

cout << setw(7) << i << "  "
     << setprecision(2) << f << left << setw(10) << str << '\n';

BONAKDARIAN:

> How would I do this in C++ in the most efficient way?

BECKER:

Not tested, but you get the idea. As I said, not as compact, but just as
powerful, and extensible. You can write your own manipulators to set up
combinations of format specifiers, for example.