Sending string over UDP in C++ - c++

Question

I would like to send a string: "Jane Doe" to intranet ip 192.168.0.4 to port 9000 over UDP. I have done this many times via UDP and TCP by Java, but now I have to do it with standard C++ libraries and I can't find any samples only topics where people just can't make it work.
I know that I have to encode "Jane Doe" as array of bytes then just open socket, pack it in datagram and send it.
C++ is not my first language and this is small part of code I can't figure out, I've chosen UDP because it is always much simpler than TCP.

Answer 1

A good source for network programming is Beej's Guide to Network Programming. Below is some sample Unix code.
If this is Windows programming:
"sock" should be of type SOCKET instead of int.
Use closesocket instead of close
#include <winsock2.h> instead of all those unix headers
#include <sys/types.h>
#include <unistd.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>
#include <memory.h>
#include <ifaddrs.h>
#include <net/if.h>
#include <errno.h>
#include <stdlib.h>
#include <iostream>
int resolvehelper(const char* hostname, int family, const char* service, sockaddr_storage* pAddr)
{
int result;
addrinfo* result_list = NULL;
addrinfo hints = {};
hints.ai_family = family;
hints.ai_socktype = SOCK_DGRAM; // without this flag, getaddrinfo will return 3x the number of addresses (one for each socket type).
result = getaddrinfo(hostname, service, &hints, &result_list);
if (result == 0)
{
//ASSERT(result_list->ai_addrlen <= sizeof(sockaddr_in));
memcpy(pAddr, result_list->ai_addr, result_list->ai_addrlen);
freeaddrinfo(result_list);
}
return result;
}
int main()
{
int result = 0;
int sock = socket(AF_INET, SOCK_DGRAM, 0);
char szIP[100];
sockaddr_in addrListen = {}; // zero-int, sin_port is 0, which picks a random port for bind.
addrListen.sin_family = AF_INET;
result = bind(sock, (sockaddr*)&addrListen, sizeof(addrListen));
if (result == -1)
{
int lasterror = errno;
std::cout << "error: " << lasterror;
exit(1);
}
sockaddr_storage addrDest = {};
result = resolvehelper("192.168.0.4", AF_INET, "9000", &addrDest);
if (result != 0)
{
int lasterror = errno;
std::cout << "error: " << lasterror;
exit(1);
}
const char* msg = "Jane Doe";
size_t msg_length = strlen(msg);
result = sendto(sock, msg, msg_length, 0, (sockaddr*)&addrDest, sizeof(addrDest));
std::cout << result << " bytes sent" << std::endl;
return 0;
}

Answer 2

This is very easy to do if you are willing to use the boost library.
Here is the code snippit
#include "boost/asio.hpp"
using namespace boost::asio;
...
io_service io_service;
ip::udp::socket socket(io_service);
ip::udp::endpoint remote_endpoint;
socket.open(ip::udp::v4());
remote_endpoint = ip::udp::endpoint(ip::address::from_string("192.168.0.4"), 9000);
boost::system::error_code err;
socket.send_to(buffer("Jane Doe", 8), remote_endpoint, 0, err);
socket.close();

Answer 3

I rewrote selbie's code to make it more C++-like and I minimized it a bit.
#include <iostream>
#include <string>
#include <arpa/inet.h> // htons, inet_addr
#include <netinet/in.h> // sockaddr_in
#include <sys/types.h> // uint16_t
#include <sys/socket.h> // socket, sendto
#include <unistd.h> // close
int main(int argc, char const *argv[])
{
std::string hostname{"192.168.0.4"};
uint16_t port = 9000;
int sock = ::socket(AF_INET, SOCK_DGRAM, 0);
sockaddr_in destination;
destination.sin_family = AF_INET;
destination.sin_port = htons(port);
destination.sin_addr.s_addr = inet_addr(hostname.c_str());
std::string msg = "Jane Doe";
int n_bytes = ::sendto(sock, msg.c_str(), msg.length(), 0, reinterpret_cast<sockaddr*>(&destination), sizeof(destination));
std::cout << n_bytes << " bytes sent" << std::endl;
::close(sock);
return 0;
}

Answer 4

For Windows, I took Mikolasan's minimised version of selbie's code and modified according to https://beej.us/guide/bgnet/html/#windows to get a small standalone example.
To get this to compile, you'll need to link the Winsock library.
#include <iostream>
#include <string>
#include <winsock2.h>
int main()
{
// Initialise Winsock DLL
// See https://beej.us/guide/bgnet/html/#windows
WSADATA wsaData;
// MAKEWORD(1,1) for Winsock 1.1, MAKEWORD(2,0) for Winsock 2.0
if (WSAStartup(MAKEWORD(1, 1), &wsaData) != 0) {
fprintf(stderr, "WSAStartup failed.\n");
exit(1);
}
// Set up connection and send
std::string hostname{ "192.168.0.4" };
uint16_t port = 9000;
SOCKET sock = ::socket(AF_INET, SOCK_DGRAM, 0);
sockaddr_in destination;
destination.sin_family = AF_INET;
destination.sin_port = htons(port);
destination.sin_addr.s_addr = inet_addr(hostname.c_str());
std::string msg = "Jane Doe";
int n_bytes = ::sendto(sock, msg.c_str(), msg.length(), 0, reinterpret_cast<sockaddr*>(&destination), sizeof(destination));
std::cout << n_bytes << " bytes sent" << std::endl;
::closesocket(sock);
// Clean up sockets library
WSACleanup();
return 0;
}