{

int serv_sock = socket(AF_INET, SOCK_DGRAM, 0);

//服务端自己的地址结构

struct sockaddr_in serv_addr;

serv_addr.sin_family = AF_INET;

serv_addr.sin_port = htons(8345);

serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);

//将 inet_ntoa() 改用 inet_ntop() 这个现代方法，支持 IPV4 和 IPV6

//printf("bind in %s : %d\n", inet_ntoa(serv_addr.sin_addr), ntohs(serv_addr.sin_port));

//INET_ADDRSTRLEN 是标识 IPV4 地址展现字符串的大小常量,INET6_ADDRSTRLEN是 IPV6 的

char serv_ip[INET_ADDRSTRLEN];

if (inet_ntop(AF_INET, &serv_addr.sin_addr, serv_ip, sizeof(serv_ip)) == NULL) {

printf("inet_ntop error\n");

close(serv_sock);

return 0;

}

printf("bind in %s : %d\n", serv_ip, ntohs(serv_addr.sin_port));

if (bind(serv_sock, (struct sockaddr*)&serv_addr, sizeof(serv_addr)) == -1) {

printf("bind error\n");

return 0;

}

//客户端的地址结构

struct sockaddr_in cli_addr;

socklen_t cli_addr_len = sizeof(cli_addr);

char buf[255];

int num = 0;

ssize_t n = recvfrom(serv_sock, buf, sizeof(buf), 0,

(struct sockaddr*)&cli_addr,

&cli_addr_len );

while (buf[0] != '\0') {

num++;

printf("recv data from %s : %d %c\n", inet_ntoa(cli_addr.sin_addr), ntohs(cli_addr.sin_port), buf[0]);

ssize_t nn = sendto(serv_sock, buf, sizeof(buf), 0,

(struct sockaddr*)&cli_addr,

sizeof(cli_addr) );

if (nn == -1)

printf("sendto error\n");

n = recvfrom(serv_sock, buf, sizeof(buf), 0,

(struct sockaddr*)&cli_addr,

&cli_addr_len );

}

printf("\nnum: %d\n", num);

close(serv_sock);

return 0;

}