[Boost-users] Re [filesystem] function to determine available space

From: Beman Dawes (bdawes_at_[hidden])
Date: 2005-09-12 21:13:06

"Sohail Somani" <s.somani_at_[hidden]> wrote in message 
news:1C1EBEF8DBACDC439D038EA051674EC709C600_at_xbox.financialcad.com...
>> -----Original Message-----
>> From: boost-users-bounces_at_[hidden]
>> [mailto:boost-users-bounces_at_[hidden]] On Behalf Of me22
>> Sent: Monday, September 12, 2005 4:36 PM
>> To: boost-users_at_[hidden]
>> Subject: Re: [Boost-users] [BULK] Re: [BULK] [filesystem]
>> function todetermineavailable space
>>
>>
>> On 12/09/05, Sohail Somani <s.somani_at_[hidden]> wrote:
>> > What about using a type that guarantees a certain amount instead of
>> > just "max" (which may vary)? Or equivalently, are we
>> guaranteed that
>> > uintmax_t can hold, say one TB, on any platform that boost supports?
>> >
>>
>> Even 1 TB isn't really safe.  I know a number of people with
>> more total storage than that.
>>
>> How about a double?  The imprecision shouldn't be a worry -- 
>> if you're beyond the range of a double's precision for free
>> space then being off by even a few MB it doesn't matter and
>> doubles are perfectly precise for small integral numbers.  (
>> on x86 linux it seems my 64-bit doubles have 53 bits of
>> mantissa meaning they're perfectly precise for anything less
>> than 8192 TeraBytes.  I don't know what the standard specifes
>> though, and my 32-bit floats are only perfectly precise for
>> under 16 MB.  That being said, even the 32-bit float has a
>> max of over 3e26 TB, so just saying the precision of the
>> number returned is dependant on the precision of your
>> platform's double would get around that, assuming of course
>> we can assure that any rounding is done on the safe side. )
>>
>> Also, the implementation could work internally in whatever it
>> wants to keep perfect precision and just feed out a double at the end.
>
> Great idea. I'm ok with this. What about platforms like linux or
> windows? What types do they use to report these stats?

64-bit integers. Every C++ compiler Boost tests run on, even really old ones 
like VC++ 6.0 and GCC2.95, have a 64-bit integral type. Mostly long long, 
but sometimes long or _int64. The C and C++ standards committees are in 
process of standardizing long long.

--Beman