Re: Force std::size_t to use __uint64

"Victor Bazarov" <>
Tue, 23 Jan 2007 14:35:54 -0500
Tom Widmer [VC++ MVP] wrote:

Victor Bazarov wrote:

Ulrich Eckhardt wrote: wrote:

Can anyone suggest a way of forcing size_t to use __uint64?
I'm using VS8 (2005) on Win32.

No. You are using a 32 bit system, i.e. pointers (and thus also
size_t) are 32 bit.

(I need a way of handling big sparse matrices in
boost::ublas::mapped_matrix which makes use of std::map<T,size_t>
(hence I the max size for a mapped_matrix is approx 65535 x 65535).
Forcing the use of __uint64 should fix this.)

Then use a map<T, uint64_t> or modify Boost, simple as that. Mucking
around with the innards of the system won't do you any good, it will
break at too many other places in return.

I just thought of one thing. If the OP is on a 32-bit system, what
chances does he have to _ever_ be able to have a batrix of more than
4 gigabytes total size? And that's assuming that the code and the
kernel mapping doesn't take any room in his process' memory and that
his T is char.

He does *need* to go 64 bits. Only then he has a chance of getting
an array or any other structure to occupy more than 4 gigs. No?

mapped_matrix is a sparse matrix (hence the fact that it uses std::map
as its back end). Only non-zero elements of the matrix take up memory.

Ah... I get it, so where 'mapped_matrix' has, say, two indices, the
underlying implementation converts them into 'size_t' using some formula,
say, i*w+j, and keeps that value as the actual key. So, it would seem
that the correct statement would be ".. makes use of std::map<size_t,T>"

The other choice for the OP then would be to somehow tell 'mapped_matrix'
what type to use for the internal index (if that's possible, I am not
familiar with Boost enough).

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