TITLE: stream output of "true" and "false" for bools

(Source: comp.lang.c++.moderated, 27 Sep 2000)

SCHWARTZ: notbob_schwartz@my-deja.com

> #include <iostream.h>

KUEHL: Dietmar Kuehl <dietmar_kuehl@yahoo.com>

This is a non-standard header. The corresponding standard header is
called <iostream>. This puts basically all names into the namespace
'std'. Thus, a corrected version of your program reads

  #include <iostream>
  int main() {
    std::cout << true << '\n';
    std::cout << false << '\n';
  }

You also don't want to write 'std::endl' instead of '\n' because the
use of 'std::endl' would unnecessarily flush the stream's buffer. This
is a bad idea unless you really want to play save and have the buffer
flushed: Flushing the buffer can become a considerable performance
problem.

SCHWARTZ:

> and yields the following output:
>
> 1
> 0

KUEHL:

Which is the correct output: By default, this is the only correct
output. If you want...

SCHWARTZ:

> true
> false

KUEHL:

you have to set 'std::ios_base::boolalpha' and use an English locale
(the default locale is such a locale):

  std::cout << std::boolalpha << true << '\n';

The manipulator 'std::boolalpha' just sets the flag, ie. you can
achieve the same result using

  std::cout.setf(std::ios_base::boolalpha);
  std::cout << true << '\n';

... and you can install a modified 'std::numpunct<char>' facet into the
used locale object to get eg. the German equivalents:

  #include <locale>
  #include <iostream>

  class german_numpunct: public std::numpunct<char> {
    string_type do_truename() const { return "wahr"; }
    string_type do_falsename() const { return "falsch"; }
  };

  int main() {
    std::locale loc;
    std::locale german_loc(loc, new german_numpunct);
    std::cout.imbue(german_loc);
    std::cout << std::boolalpha << true << ' ' << false << '\n';
  }

[snip]



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