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 != 2) {
        printf("Usage : %s <port>\n", argv[0]);
        exit(1);
    }
    srv_sock = socket(PF_INET, SOCK_DGRAM, 0);
    if (srv_sock == -1) {
        err_handler("UDP socket() error");
    }
    memset(&srv_addr, 0, 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[1]));

    if (bind(srv_sock, (struct sockaddr *) &srv_addr, sizeof(srv_addr)) == -1) {
        err_handler("bind() error");
    }

    while (1) {
        cli_adr_sz = sizeof(cli_addr);
        str_len = recvfrom(srv_sock, msg, BUF_SIZE, 0, (struct sockaddr *) &cli_addr, &cli_adr_sz);
        sendto(srv_sock, msg, str_len, 0, (struct sockaddr *) &cli_addr, cli_adr_sz);
        printf("recv and send ...\n");
    }

    close(srv_sock);
    return 0;
}

void err_handler(char *msg) {
    fputs(msg, stderr);
    fputc('\n', stderr);
    exit(1);
}

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 != 3) {
        printf("Usage : %s <IP> <PORT>\n", argv[0]);
        exit(1);
    }

    sock = socket(PF_INET, SOCK_DGRAM, 0);
    if (sock == -1) {
        err_handler("socket() error");
    }

    memset(&srv_addr, 0, sizeof(srv_addr));
    srv_addr.sin_family = AF_INET;
    srv_addr.sin_addr.s_addr = inet_addr(argv[1]);
    srv_addr.sin_port = htons(atoi(argv[2]));

    while (1) {
        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), 0, (struct sockaddr *) &srv_addr, sizeof(srv_addr));
        adr_sz = sizeof(from_addr);
        str_len = recvfrom(sock, msg, BUF_SIZE, 0, (struct sockaddr *) &srv_addr, &adr_sz);
        msg[str_len] = 0;
        printf("Msg form srv : %s", msg);
    }
    close(sock);
    return 0;
}

void err_handler(char *msg) {
    fputs(msg, stderr);
    fputc('\n', stderr);
    exit(1);
}

 build

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