Network-Programming-in-C/examples/udp_client.c

/*
* udp_client -- a datagram "client" demo
*/

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <errno.h>
#include <string.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>

#define SERVERPORT "4950"  // the port users will be connecting to

int main(int argc, char* argv[]){

    int sockfd;
    struct addrinfo hints, *servinfo, *p;
    int rv;
    int numbytes;

    if( argc != 3){
        fprintf(stderr, "usage: talker hostname message\n");
        exit(1);
    }

    memset(&hints, 0, sizeof hints);
    hints.ai_family = AF_INET6; // set to AF_INET to use IPv4
    hints.ai_socktype = SOCK_DGRAM;

    if((rv = getaddrinfo(argv[1], SERVERPORT, &hints, &servinfo)) != 0){
        fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(rv));
        return 1;
    }

    // loop throught all the results and make a socket
    for( p = servinfo; p != NULL ; p = p->ai_next){
        if((sockfd = socket(p->ai_family, p->ai_socktype,
                p->ai_protocol)) == -1){
            perror("talker: socket");
            continue;
        }

        break;
    }

    if( p == NULL ){
        fprintf(stderr, "talker: failed to create socket\n");
        return 2;
    }

    if((numbytes = sendto(sockfd, argv[2], strlen(argv[2]), 0,
        p->ai_addr, p->ai_addrlen)) == -1 ){
        perror("talker: sendto");
        exit(1);
    }

    freeaddrinfo(servinfo);

    printf("talker: sent %d bytes to %s\n", numbytes, argv[1]);
    close(sockfd);

    return 0;
}