how to cast boost byte array to a structure

Question

I am receiving incoming UDP packets in a particular structure format as bytes.

struct Packet_ {
unsigned char header;
unsigned char command;
unsigned char timecode1;
};

Now in the handle receive function i want to convert the incoming byte data to the packet structure.

boost::array<char, 1024> recv_buffer_; // Data would be received in this array should this be a char or byte array ?

void handle_receive(const boost::system::error_code& error,
        std::size_t bytes_transferred)
{
     std::string str(recv_buffer_.c_array(), bytes_transferred); // This works can i cast this to the structure ?
     Packet_ packet = (Packet_)recv_buffer_.c_array(); // Does not work



}

Also how do we cast the recceived array to the structure ?

Answer 1

I'd reverse the question. How can you read into your data structure?

struct X {
    boost::asio::io_context ioc;
    tcp::socket s{ioc};
    std::array<Packet, 32> packets;

    void demo() {
        s.connect({{},8989});

        s.async_read_some(
            boost::asio::buffer(packets),
            std::bind(&X::handle_read, this, _1, _2));
    }

    void handle_read(error_code ec, size_t transferred)
    {
        std::cout << "Received " << transferred << " bytes ("
                  << ec.message() << ")\n";
        std::cout << "First packet "           //
                  << packets[0].header << " "  //
                  << packets[0].command << " " //
                  << packets[0].timecode1      //
                  << std::endl;
    }
};

Live demo:

Live On Coliru

#include <boost/asio.hpp>
#include <boost/beast.hpp>
#include <iostream>
using boost::asio::ip::tcp;
using boost::system::error_code;
using namespace std::placeholders;

struct Packet
{
    unsigned char header;
    unsigned char command;
    unsigned char timecode1;
};

struct X {
    boost::asio::io_context ioc;
    tcp::socket s{ioc};
    std::array<Packet, 32> packets;

    void demo() {
        s.connect({{}, 8989});

        s.async_read_some(
            boost::asio::buffer(packets),
            std::bind(&X::handle_read, this, _1, _2));

        ioc.run_for(std::chrono::seconds(1));
    }

    void handle_read(error_code ec, size_t transferred)
    {
        std::cout << "Received " << transferred << " bytes ("
                  << ec.message() << ")\n";
        std::cout << "First packet "           //
                  << packets[0].header << " "  //
                  << packets[0].command << " " //
                  << packets[0].timecode1      //
                  << std::endl;
    }
};

int main() {
    X x;
    x.demo();
}

With a server:

netcat -l -p 8989 -w 1 <<< "ABCDEF"& sleep 1; ./a.out

Prints

Received 7 bytes (Success)
First packet A B C