{

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

//conn_addr 是要连接的服务器地址结构

struct sockaddr_in conn_addr;

conn_addr.sin_family = AF_INET;

conn_addr.sin_port = htons(8345);

//conn_addr.sin_addr.s_addr = inet_addr("127.0.0.1");

//将 inet_addr() 改用 inet_pton() 这个现代的方法，支持 IPV4 和 IPV6

if (inet_pton(AF_INET, "127.0.0.1", &conn_addr.sin_addr) == -1) {

printf("inet_pton error\n");

close(cli_sock);

return 0;

}

//serv_addr 是用来存储 recvfrom 中的地址结构

struct sockaddr_in serv_addr;

socklen_t serv_addr_len = sizeof(serv_addr);

char c = 1, buf[255];

int num = 0;

while (c < 100) {

sendto(cli_sock, &c, sizeof(c), 0,

(struct sockaddr*)&conn_addr,

sizeof(conn_addr) );

int n = recvfrom(cli_sock, buf, sizeof(buf), 0,

(struct sockaddr*)&serv_addr,

&serv_addr_len );

if (n > 0) {

num++;

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

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

//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(cli_sock);

return 0;

}

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

}

++c;

}

c='\0';

sendto(cli_sock, &c, sizeof(c), 0,

(struct sockaddr*)&conn_addr,

sizeof(conn_addr) );

close(cli_sock);

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

return 0;

}