Re: Double values - what precision do I use for fprintf?

["Nate Jenkins" <nate@uniwest.com>]

>> Please observe the following printf output of eighteen double variables:
>>
>> First I tried using "%20.15f" as the format string:
>>
>>  268.229220252114942    1.018511211250181
>>  66.833038547989787   12.450505533056681
>>  20.512170161382819    0.334923179252419
>>  259.358845955701327    1.571934717666495
>>  201.111247720862963    0.139476171219810
>>  270.658029698352152   -0.612280599380678
>>  105.175902698424665   -0.076345132989225
>>  343.809699615507384   -0.219206370786681
>>
>> Then I used "%30.25f":
>>
>>  268.2297152740335377529845573    1.0185111507334088098986058
>>  66.8390907719954157073516399   12.4504269834231084956854829
>>  20.5123328842112115921736404    0.3349264346316725426966343
>>  259.3596100022817267927166540    1.5719383906021777708161835
>>  201.1113154335791932680876926    0.1394751696317115263745734
>>  270.6577319741974747557833325   -0.6122834912138217511312632
>>  105.1758654981413201312534511   -0.0763454696609412730712307
>>  343.8095929658045974974811543   -0.2192182978826520134418843
>>
>> Ignoring the small differences in the two sets of data (longitude and 
>> speed of
>> eight celestial bodies computer at two different instants) I wonder - if 
>> I
>> keep increasing the number of decimal places where will it end?
>
> Shriramana,
>
> Double precision numbering format is standardized by IEEE 754 with an
> 8 byte encoding.  1 bit is used for the sign, 11 bits for the exponent
> and the remaining 52 bits are used for the precision, which means
> precision "ends" at %.52f.
>
> \Steve
>

If it is a 64-bit-floating-point data type, then isn't one supposed to use 
the "long" modifier, i.e. "%.52f" -> "%.52lf"?  Or is that not portable?

I am not concerned so much about being portable.  However, I have always 
followed the idea that "%f" is for 4 Byte floats and "%lf" is for 8 Byte 
floats or doubles...

Is that compiler specific or ????

~ Nate


"Do or do not or delegate to somebody else.  There is no try."