RE: [boost] Stream manipulators for compression, encryption, etc

From: Joe Mariadassou (JMariadassou_at_[hidden])
Date: 2001-02-15 20:35:31

> -----Original Message-----
> From: Murray, Peter C [mailto:Peter.Murray_at_[hidden]]
> Sent: Thursday, 15 February 2001 10:56 AM
> To: 'boost_at_[hidden]'
> Subject: [boost] Stream manipulators for compression, encryption, etc
> 
> 
> 
> With regard to the disussions on compression, would a more 
> elegant approach
> be to create some form of compressing stream manipulator?  I 
> admit that I am
> particularly weak on streams, so apologies if I am proposing something
> impossible...
> 
> Conceptually, I'd like to do something like this:
> 
> outfile << encrypt<DES> << compress<ZIP> << myClass;
> infile >> decrypt<DES> >> decompress<ZIP> >> myClass;
> 
> What do people think of this approach, if its even possible?
> - Peter.

One solution would be like this
class Compress
{
///some defs
}
class CompressStream: public ostream
{
// some code
};

CompressStream operator<<(ostream&,Compress&);

However the catch would be after excecuting
outfile<<Compress()<<myclass;
the compress stream adapter would be destroyed.

So a better solution would be something like this:
class CompressBuf: public streambuf
{
    streambuf& buf;
public:
   CompressBuf(streambuf& inbuf): buf(inbuf)
  {
        // other init code
   }
   //override overflow to compress the data before putting it into buf
 ///
};
which would be used as:

ofstream ofs("outfil");
CompressBuf obuf(*ofs.rdbuf());
ostream ostr(obuf);

ostr<<Mydata;

Of course you can  cascade streams like this:

ofstream ofs("outfil");
Base64Buf b64Buf(*ofs.rdbuf()); 
CompressBuf cbuf(b64Buf);
ostream ostr(cbuf);

ostr<<Mydata;
  
This should compress Mydata and convert it base64 and put it to ofs;

Developing in VC++ I must caution: 
ostr<<"\n";
puts only one character (0xa) which is not quite what I expected.

>