formatting floating point

[Saaa]

"Jarrett Billingsley" <jarrett.billingsley at gmail.com> wrote in message 
news:mailman.51.1247352795.14071.digitalmars-d-learn at puremagic.com...
> On Sat, Jul 11, 2009 at 6:44 PM, Saaa<empty at needmail.com> wrote:
>>> double d[2] = [ 0, 1, double.max];
>>> char[] c = format(d);
>>>
>>> How do I get c to represent full precision?
>>>
>>> "[0,1,1.7976931348623157e+308]" // but then with double.max being
>>> represented fully
>>
>>> You want a 309-digit number consisting mostly of 0s?
>>
>> Yes, but only if they are necessary.
>> 0 doesn't need all hose digits for instance.
>
> Um, doubles don't have infinite precision.  See those digits that it
> output?  That's all you get.  Those are the only digits that are
> necessary because those are the only digits that are *stored*.  Just
> because it's followed by almost 300 0s doesn't mean that 300 0s are
> actually stored in the number; it just means the exponent is that
> large.

I now see what you mean by 309 digits.. No I don't want that !! :D
string.format does only 6 digits by default, I added the extra double.max 
digits in myself from wikipedia :)
I overestimated the precision of a double, my bad.
(53bits != 309 digits !)
How can I format to the full number of digits, like I did for c?

>
>> What else is the point in saving doubles.
>
> If you're saving doubles in a textual format, try using the %a format
> specifier.  It outputs a float in hexadecimal notation, which is a bit
> more precise than decimal (since no rounding has to be performed).  I
> don't know if Phobos' unformatting can actually _read_ hex floats,
> though.

I could add the option, but for now I'm going for human readability