linux_c_udp_example

udp_server

 #include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
 #include <arpa/inet.h>
 #include <sys/socket.h>
 #include <stdio.h>

 #define BUF_SIZE 30

 void err_handler(char *msg);

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

     int srv_sock;
     char msg[BUF_SIZE];
     int str_len;
     socklen_t cli_adr_sz;

     struct sockaddr_in srv_addr, cli_addr;
     if (argc != ) {
         printf("Usage : %s <port>\n", argv[]);
         exit();
     }
     srv_sock = socket(PF_INET, SOCK_DGRAM, );
     if (srv_sock == -) {
         err_handler("UDP socket() error");
     }
     memset(&srv_addr, , sizeof(srv_addr));
     srv_addr.sin_family = AF_INET;
     srv_addr.sin_addr.s_addr = htonl(INADDR_ANY);
     srv_addr.sin_port = htons(atoi(argv[]));

     if (bind(srv_sock, (struct sockaddr *) &srv_addr, sizeof(srv_addr)) == -) {
         err_handler("bind() error");
     }

     while () {
         cli_adr_sz = sizeof(cli_addr);
         str_len = recvfrom(srv_sock, msg, BUF_SIZE, , (struct sockaddr *) &cli_addr, &cli_adr_sz);
         sendto(srv_sock, msg, str_len, , (struct sockaddr *) &cli_addr, cli_adr_sz);
         printf("recv and send ...\n");
     }

     close(srv_sock);
     return ;
 }

 void err_handler(char *msg) {
     fputs(msg, stderr);
     fputc('\n', stderr);
     exit();
 }

udp_client

 #include <stdlib.h>
 #include <string.h>
 #include <unistd.h>
 #include <arpa/inet.h>
 #include <sys/socket.h>
 #include <stdio.h>

 #define BUF_SIZE 30

 void err_handler(char *msg);

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

     int sock;
     char msg[BUF_SIZE];
     int str_len;
     socklen_t adr_sz;

     struct sockaddr_in srv_addr, from_addr;
     if (argc != ) {
         printf("Usage : %s <IP> <PORT>\n", argv[]);
         exit();
     }

     sock = socket(PF_INET, SOCK_DGRAM, );
     if (sock == -) {
         err_handler("socket() error");
     }

     memset(&srv_addr, , sizeof(srv_addr));
     srv_addr.sin_family = AF_INET;
     srv_addr.sin_addr.s_addr = inet_addr(argv[]);
     srv_addr.sin_port = htons(atoi(argv[]));

     while () {
         fputs("Input msg(Q to quit):", stdout);
         fgets(msg, BUF_SIZE, stdin);
         if (!strcmp(msg, "q\n") || !strcmp(msg, "Q\n")) {
             break;
         }
         sendto(sock, msg, strlen(msg), , (struct sockaddr *) &srv_addr, sizeof(srv_addr));
         adr_sz = sizeof(from_addr);
         str_len = recvfrom(sock, msg, BUF_SIZE, , (struct sockaddr *) &srv_addr, &adr_sz);
         msg[str_len] = ;
         printf("Msg form srv : %s", msg);
     }
     close(sock);
     return ;
 }

 void err_handler(char *msg) {
     fputs(msg, stderr);
     fputc('\n', stderr);
     exit();
 }

build

gcc -o usrv udp_srv.c -g -Wall
gcc -o ucli udp_cli.c -g -Wall