NetNews Usenet Archive 1993 #3/NN_1993_3.iso/spool/comp/lang/cplus/20061

Text File | 1993-01-28 | 2.6 KB | 97 lines

Newsgroups: comp.lang.c++
Path: sparky!uunet!charon.amdahl.com!amdahl!rtech!pacbell.com!ames!agate!stanford.edu!lucid.com!lucid.com!jss
From: [e-mail] (Jerry Schwarz)
Subject: Re: buffering iostreams
Message-ID: <[e-mail]>
Sender: [e-mail]
Reply-To: [e-mail] (Jerry Schwarz)
Organization: Lucid, Inc.
References:  <[e-mail]>
Date: Thu, 28 Jan 93 03:40:02 GMT
Lines: 84

In article <[e-mail]>, [e-mail] (Patrick J. Quairoli) writes:
|> i'm trying to take a long (i.e. 72) and cast it as a char so
|> that i get a value of 'H'.  this can be easily done by:
|>
|> long foo = 72;
|>
|> cout << (char)foo;
|>
|> BUT!  i also want the output to be buffered as an long (4 bytes).
|>

First, what you're talking about is generally called "padding"
not "buffering", and long's aren't normally padded to 4 characters
either.

|>
|> cout << setw(sizeof(long)) << (char)foo;
|>
|> which gives me 'H' but it is not buffered (i.e. its' flush with the
|> left of the screen and there are no trialing spaces). if it were
|> buffered as a long it would be 'H   '.
|>

Much of the documentation of iostreams says that the char inserter
pads. But the original AT&T library didn't and most (maybe all)
of the other implementations have followed the original implementation
(rather than the original documentation).

The standards committee will probably go along with the existing
implementations rather than the original documentation and say
that the char inserter doesn't pad either.

|> if i use:
|>
|> cout << setw(sizeof(long)) << foo;
|>
|> i get 72 and it is buffered with 2 leading spaces (i.e. two bytes)....
|>
|> ? how do i get a long to be cast as a char and still buffer it?
|>

One way is to use a string rather than a char.

    char a[2] ;
    a[0] = foo ;
    a[1] = 0 ;
    cout << setw(sizeof(long)) << a

If you you're going to be doing this much, you might find it convenient
to wrap it up in a manipulator.

    #include <iostream.h>
    #include <iomanip.h>

    ostream& paddedcharf(ostream& o, int c) {
        char a[2] ;
        a[0] = c ;
        a[1] = 0 ;
        return o << setw(sizeof(long)) << a ;
    }

    OAPP(int) paddedchar(paddedcharf) ;

    ...
    cout << paddedchar(foo) ;

I used an "int" manipulator rather than a "long" (as might
be suggested by the original problem) because iomanip.h declares
it.

And finally with regard to whether padding comes before
or after the value.  This can be controlled by flags.  To get
the padding after the data instead of before (the default is
before) you do

    cout.setf(ios::left,ios::adjustfield) ;

The flag specifies where the data goes.

   -- Jerry Schwarz