[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<briqueabraque at 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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