<p>Can Spirit (part of Boost C++ library) be used to parse out binary data coming from a stream?  For example, can it be used to parse data coming from a socket into structures, bytes, and individual bit flags?  Thanks!</p>

Boost Spirit allows for a parser to be defined using
Extended Backus–Naur Form (EBNF)
syntax with
template meta-programming
. It is very flexible and uses abstract classes in all phases of the parsing process that can be customized. In order to process a binary data stream, you would need to implement custom scanner classes since the default types are tailored for text input. You can read further in
The Scanner and Parsing
section of the
Spirit User's Guide
.
In my humble opinion, binary data streams are best handled with hand rolled serialization code. Spirit is geared more towards well formed grammars like mark-up or scripting languages. For example,
The Complete Syntax of Lua
is provided in EBNF. So, it might make sense to use Spirit to build a custom parser. On the other hand, a proprietary serial data link with synchronization bytes and CRC bracketing messages would require a lot more work just to define the EBNF if a
context-free grammar
even exists for it.
Addendum
The latest version of Boost Spirit includes functionality for dealing with binary data.