From: Waldemar Schultz <schultz AT ma DOT tum DOT de>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: DJGPP reserves wrong int size
Date: Fri, 29 Jun 2001 11:59:59 +0200
Organization: [posted via] Leibniz-Rechenzentrum, Muenchen (Germany)
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Eli Zaretskii wrote:
> They work for me, in GCC 2.95.3.  (I didn't use 2.95.2 long enough to
> tell.)
> 
> For long doubles, the right format for debugging printf's is "%.19g".
      ^^^^                                                     "%.19Lg"
right?
> Note: "g", not "f", because you want 19 significant digits, not 19
> digits after the dot (think about a number like 123456789.987654321).
> 
> For the same reason, I suggest to use "%.16g" for doubles.
> 
> > I am somewhat curious as to how printf
> > knows the format of a double or for that matter int you pass it
> > however.
> 
> It doesn't; it simply assumes that the format specifier tells the
> truth.  That is, if you say "%f", the corresponding argument is a
> double, and if you say "%Lf", it's a long double.
so IMHO the libc info pages about printf/scanf are wrong.
(at least for DJGPP + gcc)

scanf():
    `Le'
    `LE'
    `lle'
    `llE'
    `Lf'
    `LF'
    `llf'
    `llF'
    `Lg'
    `LG'
    `llg'
    `llG'
          Convert the input to a `long double'.

printf():
    `e'
    `E'
          A floating point number (double or long double).  The
          exponent case matches the specifier case.  The representation
          always has an exponent.

    `f'
          A floating point number (double or long double).  The
          representation never has an exponent.

    `g'
    `G'
          A floating point number (double or long double).  The
          exponent case matches the specifier case.  The representation
          has an exponent if it needs one.

-- 
 Gruss Waldemar Schultz.         schultz AT ma DOT tum DOT de
 Technische Universität München, Zentrum Mathematik M1, D 80290 München
 Tel: +49 (0)89 2892 8226        FAX: +49 (0)89 2892 8228