[Haskell-cafe] Re: FFI to double constants, printf

[Maurí­cio]

That helps, but:

#include <stdio.h>
#include <math.h>
int main ()
{
  long double d = HUGE_VAL;
  printf("%.30Lf\n", d);
}

still prints just (as it should, I think):

inf

Is there maybe some way to check if a double or
long double do have a "proper" value?

You probably want something like printf("%.10Lg",d);. Here's a shot C
example and its output:

#include <stdio.h>

int main(int argc, char * argv[])
{
    long double d = 0.123456789;

    printf("%.30Lf\n", d);
    printf("%.20Lg\n", d);
    printf("%.20Le\n", d);
}

/*
0.123456788999999997336054491370
0.12345678899999999734
1.23456788999999997336e-01
*/

On Fri, Jul 17, 2009 at 6:41 PM, Maurí­cio<briqueabra...@yahoo.com> wrote:

When we printf doubles from C (like when using hsc2hs to bind to a
constant) we can get something that's not valid Haskell. See these
2 examples:

3.40282347e+38F

inf

Do you know some way to printf a double using printf (or any other
standard function) that's always going to give me valid Haskell
text, even in special cases?

Thanks,
Maurício

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