Re: [boost] persistent vector

From: Beman Dawes (bdawes_at_[hidden])
Date: 2001-07-27 10:50:37

At 07:42 PM 7/26/2001, Greg Chicares wrote:
 >[Have you examined the persistency stuff in the files area?]
 >
 >Paul Mclachlan wrote:
 >>
 >> At 17:46 07 Jul 2001 -0000, michel.andre_at_[hidden] wrote:
 >>
 >> > Would there be any interest in an persistent vector with the exact
 >> > same interface as std::vector that stores it's data in a persistent
 >> > file? Preferably implemented using memory mapped files on plattforms
 >> > were they are supported.
 >> >
 >> > Of course there are restrictions on the data contained in such a
 >> > vector it may not contain any dynamically allocated data or pointers.
 >
 >This seems to focus on the container rather than its elements. Is this
 >intended mainly as a C++ wrapper around memory-mapped files, rather than
 >as a more general object persistency framework?
 >
 >> I handle endian-ness issues (at present) with a wrapper type (either BE 

 >or
 >> LE) that stores into the appropriate binary format and converts from it 

 >on
 >> every read.
 >[...]
 >> Reading the file back in is as simple as mmap() and casting the pointer 

 >to
 >> the start to an object of the appropriate time.  This is a speed
 >advantage
 >> when compared to marshalling (serializing?) to disk.
 >
 >How great a speed advantage do you get by using a binary format?
 >'0x4000c90fdaa22168c235' is faster, but '3.14159265358979323846L'
 >works on more machines and produces a human-readable file. Would
 >it make sense to use a portable character representation first,
 >then examine performance enhancements later?

You might want to look at the persistence work-in-progress in the Boost 
CVS. It addresses those issues.  There has been a suggestion that 
"serialize" might be a better name.

http://cvs.sourceforge.net/cgi-bin/viewcvs.cgi/~checkout~/boost/boost/libs/persistence/doc/Attic/persistence.html?rev=HEAD&content-type=text/html&only_with_tag=MAIN&hideattic=0

--Beman