Sending string over UDP in C++

c++, sockets, udp

Solution

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;

}

Problem

Original source

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