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

int main(int argc, char **argv)
{
struct sockaddr_in s_addr;
struct sockaddr_in c_addr;
int sock;
socklen_t addr_len;
int len;
char buff[128];

/* 創(chuàng)建 socket , 關(guān)鍵在于這個 SOCK_DGRAM */
if ((sock = socket(AF_INET, SOCK_DGRAM, 0)) == -1) {
perror("socket");
exit(errno);
} else
printf("create socket.\n\r");

memset(&s_addr, 0, sizeof(struct sockaddr_in));
/* 設(shè)置地址和端口信息 */
s_addr.sin_family = AF_INET;
if (argv[2])
s_addr.sin_port = htons(atoi(argv[2]));
else
s_addr.sin_port = htons(7838);
if (argv[1])
s_addr.sin_addr.s_addr = inet_addr(argv[1]);
else
s_addr.sin_addr.s_addr = INADDR_ANY;

/* 綁定地址和端口信息 */
if ((bind(sock, (struct sockaddr *) &s_addr, sizeof(s_addr))) == -1) {
perror("bind");
exit(errno);
} else
printf("bind address to socket.\n\r");

/* 循環(huán)接收數(shù)據(jù) */
addr_len = sizeof(c_addr);
while (1) {
len = recvfrom(sock, buff, sizeof(buff) - 1, 0,
(struct sockaddr *) &c_addr, &addr_len);
if (len < 0) {
perror("recvfrom");
exit(errno);
}

buff[len] = '\0';
printf("收到來自%s:%d的消息:%s\n\r",
inet_ntoa(c_addr.sin_addr), ntohs(c_addr.sin_port), buff);
}
return 0;
}

客戶端源代碼如下：

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


int main(int argc, char **argv)
{
struct sockaddr_in s_addr;
int sock;
int addr_len;
int len;
char buff[128];

/* 創(chuàng)建 socket , 關(guān)鍵在于這個 SOCK_DGRAM */
if ((sock = socket(AF_INET, SOCK_DGRAM, 0)) == -1) {
perror("socket");
exit(errno);
} else
printf("create socket.\n\r");

/* 設(shè)置對方地址和端口信息 */
s_addr.sin_family = AF_INET;
if (argv[2])
s_addr.sin_port = htons(atoi(argv[2]));
else
s_addr.sin_port = htons(7838);
if (argv[1])
s_addr.sin_addr.s_addr = inet_addr(argv[1]);
else {
printf("消息必須有一個接收者！\n");
exit(0);
}

/* 發(fā)送UDP消息 */
addr_len = sizeof(s_addr);
strcpy(buff, "hello i'm here");
len = sendto(sock, buff, strlen(buff), 0,
(struct sockaddr *) &s_addr, addr_len);
if (len < 0) {
printf("\n\rsend error.\n\r");
return 3;
}

printf("send success.\n\r");
return 0;
}

編譯程序用下列命令：

gcc -Wall simple-udpserver.c -o server
gcc -Wall simple-udpclient.c -o client

運行程序用下列命令：

./server 127.0.0.1 7838

./client 127.0.0.1 7838

UDP方式廣播通訊
源代碼變成下面的：

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

int main(int argc, char **argv)
{
struct sockaddr_in s_addr;
int sock;
int addr_len;
int len;
char buff[128];
int yes;

/* 創(chuàng)建 socket */
if ((sock = socket(AF_INET, SOCK_DGRAM, 0)) == -1) {
perror("socket");
exit(errno);
} else
printf("create socket.\n\r");

/* 設(shè)置通訊方式對廣播，即本程序發(fā)送的一個消息，網(wǎng)絡(luò)上所有主機均可以收到 */
yes = 1;
setsockopt(sock, SOL_SOCKET, SO_BROADCAST, &yes, sizeof(yes));
/* 唯一變化就是這一點了 */

/* 設(shè)置對方地址和端口信息 */
s_addr.sin_family = AF_INET;
if (argv[2])
s_addr.sin_port = htons(atoi(argv[2]));
else
s_addr.sin_port = htons(7838);
if (argv[1])
s_addr.sin_addr.s_addr = inet_addr(argv[1]);
else {
printf("消息必須有一個接收者！\n");
exit(0);
}

/* 發(fā)送UDP消息 */
addr_len = sizeof(s_addr);
strcpy(buff, "hello i'm here");
len = sendto(sock, buff, strlen(buff), 0,
(struct sockaddr *) &s_addr, addr_len);
if (len < 0) {
printf("\n\rsend error.\n\r");
return 3;
}

printf("send success.\n\r");
return 0;
}

編譯這個程序用下列命令：