Subject: Re: [Boost-users] [serialization] appending elements
From: Robert Ramey (ramey_at_[hidden])
Date: 2009-03-09 00:47:41
Agustín K-ballo Bergé wrote:
> Is it possible to append serialized elements to an existing archive?
the serialization library doesn't currently address this situation.
>I
> need to keep a set of records on a file, and periodically add new
> entries to it (kind of like a database table). Reading the whole set,
> adding the new records, and serializing the set back is not an option
> since I expect the set to go pretty big.
I understand and sympathise.
> I have tried to keep several archives at the same stream (with
> no_header and no_tracking flags),
I believe this might be made to work.
> but then I don't know how to read
> them. Reading them as if they were a single archive does not work,
> should it?
no.
Here's an idea.
// append a bunch of archives to a file
main(..){
ofstream os(..); // open for append
{
oarchive oa(os)
oa << a bunch of stuff
} // close archive leaving stream open
{
oarchive oa(os)
oa << a bunch of other stuff
} // close second archive
} // now we have a closed stream with several self-contained archives in it
// read a bunch of archives from one file
main(..){
ifstream is(...); // open the normal way
{
iarchive ia(..); // open first archive
ia >> first bunch of stuff
} // close first archive leaving stream open
{
iarchive ia(..); // open first archive
ia >> second bunch of stuff
} // close second archive leaving stream open
} // close input stream
exercise for the reader. Figure out where to save the Number of archives
inthe
file. A couple of ideas
1) a separate companion file
2) save a few bytes at the beging of the file - call this archive count.
Update this
after every "append" and read it duning load.
Good Luck with this.
Robert Ramey
main(..
>
> Agustín K-ballo Bergé.-