[Boost-users] [iostreams] Any simple examples on implementing a Symmetric_filter?

From: eg (egoots_at_[hidden])
Date: 2006-11-29 21:56:07

Hi all,

I'm new to the iostreams library. It looks pretty cool.
We have a bunch of existing objects which already have interfaces for 
reading and writing their state to a stream, e.g.
MyWrite(std::ostream &out) and  MyRead(std::istream &in)

I've convinced myself I can filter these with iostreams, as I prototyped 
setting up a filtering stream with an existing gzip_compressor() filter, 
then reversed it with a gzip_decompressor(). Nice.

Now, what I want to do is write my own filter, and thought that a 
symmetric_filter met my needs based on the description. Unfortunately, 
there are no simple examples in the tutorial section, and the 
documentation seems a bit weaker in this area. As a first kick at the 
can, reading the zlib/bzip implementations is a bit dense to pick out 
the nuances.

Does anyone have an identity_filter example (based on symmetric_filter) 
that just copies input to output characters?

... or given some dumb c function like the following, how to construct a 
symmetric_filter using it.

my_dumb_crypt(char* in, char* out, char *pwd, int len)
{
   for (int i=0; i < len; ++i) // assumes in, out, and pwd are len long
     out[i] = in[i]  ^ pwd[i];

}

Thanks.
eg