#include <sys/types.h>
#include <sys/socket >
ssize_t sendto(int sockfd, const void *buf, size_t len, int flags,const struct sockaddr *dest_addr, socklen_t addrlen);
	- 参数：
		- sockfd : 通信的fd
		- buf : 要发送的数据
		- len : 发送数据的长度
		- flags : 0
		- dest_addr : 通信的另外一端的地址信息
		- addrlen : 地址的内存大小
	
ssize_t recvfrom(int sockfd, void *buf, size_t len, int flags,struct sockaddr *src_addr, socklen_t *addrlen);
	- 参数：
		- sockfd : 通信的fd
		- buf : 接收数据的数组
		- len : 数组的大小

		- flags : 0
		- src_addr : 用来保存另外一端的地址信息，不需要可以指定为NULL
		- addrlen : 地址的内存大小

udp_server.c

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

int main() {
    // 1.创建一个通信的socket
    int fd = socket(PF_INET,SOCK_DGRAM,0);
    if(fd == -1) {
        perror("socket");
        exit(-1);
    }
    // 2.绑定
    struct sockaddr_in saddr;
    saddr.sin_family = AF_INET;
    saddr.sin_port = htons(9999);
    saddr.sin_addr.s_addr = INADDR_ANY;
    int ret = bind(fd,(struct sockaddr*)&saddr,sizeof(saddr));
    if(ret == -1) {
        perror("bind");
        exit(-1);
    }
    // 3.通信 
    while (1) {
        char recvbuf[128] = {0};
        char ipbuf[16] = {0};
        struct sockaddr_in caddr;
        int len = sizeof(caddr);
        // 接收数据
        int num = recvfrom(fd,recvbuf,sizeof(recvbuf),0,(struct sockaddr*)&caddr,&len);
        if(num == -1) {
            perror("recvfrom");
            exit(-1);
        }
        inet_ntop(AF_INET,(struct sockaddr*)&caddr.sin_addr.s_addr,ipbuf,sizeof(ipbuf));
        printf("Client IP : %s,Port : %d\n",ipbuf,ntohs(caddr.sin_port));

        printf("client say : %s\n",recvbuf);

        // 发送数据
        sendto(fd,recvbuf,strlen(recvbuf) + 1,0,(struct sockaddr*)&caddr,sizeof(caddr));
    }
    close(fd);
    return 0;
}

udp_client.c

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

int main() {
    // 1.创建一个通信的socket
    int fd = socket(PF_INET,SOCK_DGRAM,0);
    if(fd == -1) {
        perror("socket");
        exit(-1);
    }

    // 服务器的地址信息
    struct sockaddr_in saddr;
    saddr.sin_family = AF_INET;
    saddr.sin_port = htons(9999);
    inet_pton(AF_INET,"127.0.0.1",&saddr.sin_addr.s_addr);

    int num = 0;
    // 3.通信 
    while (1) {
        // 发送数据
        char sendBuf[128] = {0};
        sprintf(sendBuf,"hello,i am client %d \n",num++);
        sendto(fd,sendBuf,strlen(sendBuf) + 1,0,(struct sockaddr*)&saddr,sizeof(saddr));

        // 接收数据
        int num = recvfrom(fd,sendBuf,sizeof(sendBuf),0,NULL,NULL);
        printf("server say : %s\n",sendBuf);

        sleep(1);
    }
    close(fd);
    return 0;
}

heheda@heheda:~/Linux/lesson37$ gcc udp_server.c -o server
heheda@heheda:~/Linux/lesson37$ ./server
Client IP : 127.0.0.1,Port : 34127
client say : hello,i am client 0 

Client IP : 127.0.0.1,Port : 34127
client say : hello,i am client 1 

Client IP : 127.0.0.1,Port : 34127
client say : hello,i am client 2 

Client IP : 127.0.0.1,Port : 34127
client say : hello,i am client 3 

Client IP : 127.0.0.1,Port : 34127
client say : hello,i am client 4 

Client IP : 127.0.0.1,Port : 53230
client say : hello,i am client 0 

Client IP : 127.0.0.1,Port : 34127
client say : hello,i am client 5 

Client IP : 127.0.0.1,Port : 53230
client say : hello,i am client 1 

Client IP : 127.0.0.1,Port : 34127
client say : hello,i am client 6 

Client IP : 127.0.0.1,Port : 53230
client say : hello,i am client 2 

Client IP : 127.0.0.1,Port : 34127
client say : hello,i am client 7 

Client IP : 127.0.0.1,Port : 53230
client say : hello,i am client 3 

Client IP : 127.0.0.1,Port : 34127
client say : hello,i am client 8 

Client IP : 127.0.0.1,Port : 53230
client say : hello,i am client 4 

Client IP : 127.0.0.1,Port : 34127
client say : hello,i am client 9 

Client IP : 127.0.0.1,Port : 53230
client say : hello,i am client 5 

Client IP : 127.0.0.1,Port : 34127
client say : hello,i am client 10 

Client IP : 127.0.0.1,Port : 53230
client say : hello,i am client 6 

Client IP : 127.0.0.1,Port : 34127
client say : hello,i am client 11 

Client IP : 127.0.0.1,Port : 53230
client say : hello,i am client 7 

Client IP : 127.0.0.1,Port : 34127
client say : hello,i am client 12 

Client IP : 127.0.0.1,Port : 53230
client say : hello,i am client 8 

Client IP : 127.0.0.1,Port : 34127
client say : hello,i am client 13 

Client IP : 127.0.0.1,Port : 53230
client say : hello,i am client 9 

Client IP : 127.0.0.1,Port : 34127
client say : hello,i am client 14 

Client IP : 127.0.0.1,Port : 53230
client say : hello,i am client 10 

Client IP : 127.0.0.1,Port : 34127
client say : hello,i am client 15 

Client IP : 127.0.0.1,Port : 53230
client say : hello,i am client 11