Re: [Boost-users] Can boost help me organize/parse lots of binary data?

Subject: Re: [Boost-users] Can boost help me organize/parse lots of binary data?
From: Antony Polukhin (antoshkka_at_[hidden])
Date: 2013-02-21 09:15:17

This looks like a perfect place for Boost.Variant. Here is some pseudo code:

#include <boost/variant.hpp>

struct DecoderVisitor: boost ::static_vizitor<> {
istream& Stream;

explicit DecoderVisitor(istream& Stream): Stream(Stream){}

void operator()(String& s) const {
s.Decode(Stream);
}

void operator()(Double& d) const {
d.Decode(Stream);
}

// or you may just write
// template <class T>
// void operator()(T& val) const {
// val.Decode(Stream);
//}
};

  class EmployeePacket
   {
typedef boost::variant<String, Double> variant_t;
     std::vector<variant_t> Items;

     EmployeePacket()
     {
       Items.push_back(String("name", "John Doe"));
       Items.push_back(Double("salary", "USD", 1, 1));
     }

     void Decode(istream& Stream)
     {
       for (auto pItem : Items)
boost::apply_visitor(DecoderVisitor(Stream), pItem)
     }

     double GetSalary()
     {
       return boost::get<Double>(Items[1]).value;
     }
   }

 class Double
 {
   string name;
   string units;
 //  double decode_conversion_scale;
 //  double decode_conversion_translate;
 //  unsigned number_of_bits_used_to_encode
 //  double scale_factor
   double value;
   void Decode(istream& Stream)
    {
     Stream.read(&value, 8);
     value = value * decode_conversion_scale + decode_conversion_translate;
  }

   class String
   {
     string name;
     string value;
     void Decode(istream& Stream);
   }

Advantages are:
* less calls to new => faster code
* no raw pointers => much safer
* no virtual functions and dynamic casts => much faster and safer
* you exactly specify which types will be stored in variant => more
compile time checks

And Boost.Variants documentation is not big and it is a simple enough library.

--
Best regards,
Antony Polukhin