Re: C++ Primer 4/e exercise 1.19

 James Kanze <>
Thu, 12 Jul 2007 10:02:04 -0000
On Jul 12, 10:30 am, Erik Wikstr=F6m <> wrote:

On 2007-07-12 10:01, arnuld wrote:


BTW, how can i make the output equally dispersed ? in C i can use "%.
2d". what in C++ ?

Take a look at ostream.width(), and ostream.fill(), beware though, the
settings reset after each output. People can say what they want but
printf() beats the shit out of C++ streams when it comes to formated
output of simple data types.

People can say what they will, but C++ streams are far easier
and more intuitive for just about any formatting. (Actually,
neither is very intuitive, and the one you know best is
generally the simpler. iostream is probably simpler to learn,
however, in addition to being the safest and the most
extendable.) In this case:

    std::cout << std::setw( 2 ) << n ;

does the job. Except, of course, that he doesn't want 2,
because the user might have input 1001, 1020. He needs

    width = ciel( log10( upper ) ) ;
    // ...
    std::cout << std::setw( width ) << n ;

And FWIW: width is volatile, and gets reset each time around;
the other values (like fill) aren't, and it is the fact that
they don't get reset which often causes problems.

(As an interesting exercise, compare:
    printf( "%*d", ciel( log10( upper ), i ) ;
    std::cout << std::setw( ciel( log10( upper ) ) ) << i ;
Why does one work, and the other not:-)?)

James Kanze (GABI Software)
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