Question about Boost.Asio

[benbalach]

As I was reading the documentation and I noticed that you can only send data that is continuously allocated (such as a plain C style array of characters).

My question is, how would I go about sending and receiving an object of a user-defined type? (such as:)

#include <vector>
#include <pair>

class A
{
    std::vector<std::pair<int, std::vector<char>> data;
};

Sure I could convert an pointer to an object of type A to a void*, but the data is not continuous in memory.

This is how I picture the memory structure of an object of type A:
http://postimg.org/image/fwvo47ogd/

[MiiNiPaa]

Class members are continuously allocated (but some of the members could be pointers pointing to another memory areas)

Sending and receivin should be handled as reading and writing from file: you need a method to convert your class to platform-agnostic sequence of binary digits. This process is called serialization.
For example structure of your serialized class might be:
4 bytes of unsigned big endian (network order) number denoting number of elements in outer vector (X)
X entries of outer vector elements
Each element:
4 bytes of signed big endian number (first element of pair)
4 bytes of unsigned big endian number denoting number of elements in intter vector (Y)
Y entries of char (1 byte)  
You will need to make sure that actual vector sizes/values of int is not larger than serialized value can hold and that your vector/int can hold deserialized value.

[JLBorges]

Stringify the object and send the sequence of characters. Unstringify at the other end.
Something like:

struct A
{
    std::vector< std::pair< int, std::vector<char> > > data;
};

std::string stringify( const A& a )
{
    std::ostringstream stm ;

    for( const auto& pair : a.data ) // for each pair
    {
        stm << pair.first << '\n' ; // int, newline
        for( char c : pair.second ) stm << c ; // vector of chars
        stm << '\n' ; // newline (assumes that the sequence of char does not contain newline)
    }
    stm << '\n' ; // end with a double newline

    return stm.str() ;
}

A from_string( const std::string& stringified ) ; // TODO 

For something more elaborate,
http://www.boost.org/doc/libs/1_57_0/libs/serialization/doc/index.html

[benbalach]

@MiiNiPaa
@JLBorges

Thank you so much!