Re: [Boost-users] size_type doubts / integer library..

From: Chris Jefferson (chris_at_[hidden])
Date: 2008-08-18 15:31:17

2008/8/18 Andrea Denzler <andrea_at_[hidden]>:
>> So at least on a local scale, index values do correspond to memory
>> addresses or memory offsets.
>
> Sure, A part from STL and other containers using they own operator, when you
> use direct memory access a index is used to access the flat memory of the
> allocated object/array.
>
>> > The "problem" could be solved by using largest _signed_ type both for
>> size_type and difference_type.
>> [snip]
>> > So I'd advocate signed representation for size_type and difference_type.
>
> Sure, also because when you play with pointers you have negative indexes
> too. So a signed index is welcome, and it should cover the range of the
> maximum memory size of an object (not the entire memory).
>
> But on a 32 bit architecture where theorically I can allocate up to 4
> Gigabyte for a single object using a signed integer requires a 32bit + sign
> = 33 bits. Ops... what now?
> A) using signed 32bit, so the memory address swaps between -2^31 and
> +2^31-1. Not exactly elegant.
> B) using unsigned 32 bit, a contingous address from 0 to +2^32.
> C) using a bigger integral signed type, probably a 64 bit signed.
> And 2 GByte is not that uncommon...

I believe (I checked some time ago) that you cannot allocate an object
of size 2GB on any 32-bit OS that I could get my hands on. Do you know
of any place where you can?

Chris