Re: [Dev-C++] RES: Reading and printing long double values

[Per W. <pw...@ia...>]

Yes, we are well aware that the MinGW compiler supports the long double
data type as distinct from the double type.

But the big question is: Why do you _need_ to print long double values?
The double data type has 15 significant digits - is this really too
little?

The biggest reason for the long double data type is to get improved
precision for internal values in numeric algorithms, where you may sum a
nuge number of small numbers or where you may subtract similarly sized
numbers and get calcellation effects.

Most situations where the end result is expected to have 20 or more
significant digits are well suited for big-number libraries and
fixed-point arithmetic. Then you can produce results with 1000 or 1000000
significant digits if you want to.

It doesn't matter how large fp data types you have available - floating
point numbers can not store most values without rounding errors, and the
conversion from binary format to decimal format done by printf() will
result in rounding. The only question is how many correctly rounded digits
you get.

All you need to do to print your long double values are simple typecasts
in the printf() calls.

Your next alternative is to switch to cygwin instead. The cygwin library
supports %Lg for printing extended-precision floating-point values.
However, you must distribute your application with the cygwin support dll.

/pwm

On Wed, 30 Apr 2008, André Macário Barros wrote:

>    But MigGW does this distinction.
>
>    Please try:
>       printf(sizeof(double))      and
>       printf(sizeof(long double))
>
>    Does anybody know who wrote a printf or
> a full stdio.h (fprintf, sprintf, etc) which
> supports long doubles for MingGW?
>
> Regards
> André
>
>
> -----Mensagem original-----
> De: Per Westermark [mailto:pw...@ia...]
> Enviada em: terça-feira, 29 de abril de 2008 02:39
> Para: André Macário Barros
> Cc: Lista do Dev-C++
> Assunto: Re: [Dev-C++] Reading and printing long double values
>
>
> MinGW is using the M$ libraries, so to my knowledge it isn't possible to
> print a long double using printf().
>
> Note that M$ does not distinguish between double and long double, so they
> don't have a need for a long double formatting prefix.
>
> /pwm
>
> On Sun, 27 Apr 2008, André Macário Barros wrote:
>
> > Dear users,
> >
> >    I´m having some problems trying to read/print
> > a long double value in C.
> >
> >    Based on a documentation I´ve found, one of the
> > attempts was:
> >
> >    ...
> >    long double var=3.0;
> >    ...
> >    printf("printing a long double value-->%5.0Lg\n", var);
> >    ...
> >
> >    I´ve already tested: %LE and %LF and none of these
> > options worked.
> >
> >    Does anybody know how to read and print?
> >    Thanks!
> >
> > Andre
> >
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