Question

I have a header field of 2 bytes where first four bits are packet type and other 12 bits are for length. but i don’t know how to store this values and retrieve them.

I am using ms c++ for client and java for server. It is the client which has to set this values and server has to retrieve it.

Thanks

Answer 1

Storing

unsigned short get_header(unsigned char type, unsigned short length)
{
  return (static_cast<unsigned short>(type) << 12) | length;    
}

Retrieving (from unsigned short)

unsigned short header = /* get 2 header bytes */
unsigned char type = header >> 12;
unsigned short length = header & 0xFFF;

Retrieving (from unsigned char[2])

unsigned char bytes[2] = /* get 2 header bytes */
unsigned char type = bytes[0] >> 4;
unsigned short length = bytes[0] & 0xF | bytes[1];