网络编程 udp 发送端 bind 作用

运行方法：先运行【1，先接收再发送】，再运行【2，先发送再接收】

1，先接收再发送：

#include <stdio.h> #include <unistd.h> #include <sys/types.h> #include <sys/socket.h> #include <netinet/in.h> #include <arpa/inet.h> #include <string.h> #include <netdb.h>//getaddrinfo  int main(){   int sock;   sockaddr_in addr;   sockaddr_in senderinfo;   socklen_t addrlen;   char buf[2048];   char senderstr[16];   int n;    sock = socket(af_inet, sock_dgram, 0);    addr.sin_family = af_inet;   addr.sin_port = htons(12345);   addr.sin_addr.s_addr = inaddr_any;   bind(sock, (sockaddr*)&addr, sizeof(addr));    while(1){     memset(buf, 0, sizeof(buf));      addrlen = sizeof(senderinfo);     n = recvfrom(sock, buf, sizeof(buf) - 1, 0,          (sockaddr*)&senderinfo, &addrlen);      inet_ntop(af_inet, &senderinfo.sin_addr, senderstr, sizeof(senderstr));     printf("recvfrom: %s, port=%dn", senderstr, ntohs(senderinfo.sin_port));          sendto(sock, buf, n, 0, (sockaddr*)&senderinfo, addrlen);      printf("send data to: %s, port=%dn", senderstr, ntohs(senderinfo.sin_port));        } } 

执行方式：

g++ -g udp_recv_send.cpp -std=c++11 -o se ./re

2，先发送再接收：

#include <stdio.h> #include <unistd.h> #include <sys/types.h> #include <sys/socket.h> #include <netinet/in.h> #include <arpa/inet.h> #include <string.h> #include <netdb.h>//getaddrinfo  void print_port_num(int sock){   sockaddr_in s;   socklen_t sz = sizeof(s);   getsockname(sock, (sockaddr*)&s, &sz);   printf("%dn", ntohs(s.sin_port)); } int main(int argc, char* argv[]){   int sock;   sockaddr_in addr;   sockaddr_in senderinfo;   socklen_t senderinfolen;   int n;   char buf[2048];   sockaddr_in myname;      if(argc != 2){     return 1;   }    sock = socket(af_inet, sock_dgram, 0);    addr.sin_family = af_inet;   addr.sin_port = htons(12345);   inet_pton(af_inet, argv[1], &addr.sin_addr.s_addr);       myname.sin_family = af_inet;   myname.sin_addr.s_addr = inaddr_any;   myname.sin_port = htons(34567);   bind(sock, (sockaddr*)&myname, sizeof(myname));       n = sendto(sock, "hello", 5, 0, (sockaddr*)&addr, sizeof(addr));   if(n < 1){     perror("sendto");     return 1;   }    print_port_num(sock);    memset(buf, 0, sizeof(buf));   senderinfolen = sizeof(senderinfo);   recvfrom(sock, buf, sizeof(buf), 0,        (sockaddr*)&senderinfo, &senderinfolen);    printf("%sn", buf);    close(sock);    return 0; } 

./a.out 127.0.0.1