From: Hans-Bernhard Broeker <broeker AT physik DOT rwth-aachen DOT de>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Iostream question
Date: 30 Apr 2001 13:25:51 GMT
Organization: Aachen University of Technology (RWTH)
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Rafal Maj <maj_rafal AT poczta DOT onet DOT pl> wrote:
> Hi,
> following code :
>   long double r =
> 3.1415012345678901111112222233333444445555666677777888899999000012345;
>   cerr << setprecision(999) << r;
> displays in cerr only : 3.1415012345678903
> How to display (or write to file) long double with full precision using
> iostream ? Or does long double hold only 16 digits of my variable ?

Long double holds more than 16 digits, but your way of initializing doesn't
give it more than 16, I think. The problem is that your constant isn't
flagged as a long double, and thus may be interpreted as a double.
Try:

  long double r = 3.1415012345678901111112222233333L;

There's no good reason to provide that many (or even more) digits ---
even long double stores only around 20 (LDBL_EPSILON is 1.08e-19,
roughly). The "L" suffix is important, because of this (taken from the
C99 standard draft):

       [#4]  An  unsuffixed  floating constant has type double.  If
       suffixed by the letter f  or  F,  it  has  type  float.   If
       suffixed by the letter l or L, it has type long double.






-- 
Hans-Bernhard Broeker (broeker AT physik DOT rwth-aachen DOT de)
Even if all the snow were burnt, ashes would remain.