C语言 c - udp 在同一个套接字上发送和接收
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c - udp send and receive on the same socket
提问by user3574984
I would like to send and receive packets on the same socket, is it possible or I have to create two socket, one to send and one to receive? If yes, can you give me an example?
我想在同一个套接字上发送和接收数据包，是否可能或者我必须创建两个套接字，一个发送一个接收？如果是的话，你能给我举个例子吗？
Another question: how can I get the source ip from a received packet?
另一个问题：如何从接收到的数据包中获取源 ip？
EDIT (code example):
编辑（代码示例）：
int main(void) {
struct sockaddr_in si_me, si_other;
int s, i, slen=sizeof(si_other);
char buf[BUFLEN];
if ((s=socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP))==-1)
die("socket");
memset((char *) &si_me, 0, sizeof(si_me));
si_me.sin_family = AF_INET;
si_me.sin_port = htons(1234);
si_me.sin_addr.s_addr = htonl(192.168.1.1);
if (bind(s, &si_me, sizeof(si_me))==-1)
die("bind");
if (recvfrom(s, buf, BUFLEN, 0, &si_other, &slen)==-1)
diep("recvfrom()");
printf("Data: %s \nReceived from %s:%d\n\n", buf, inet_ntoa(si_other.sin_addr), ntohs(si_other.sin_port));
//now I want the server to answer back to the client
close(s);
return 0;
}
回答by Remy Lebeau
Yes, you can use the same socket for sending and receiving. recvfrom()tells you the IP/port of the sender. Simply sendto()that IP/port using the same socket that you use with recvfrom(), eg:
是的，您可以使用相同的套接字进行发送和接收。recvfrom()告诉您发件人的 IP/端口。简单地sendto()使用与您一起使用的相同套接字的 IP/端口recvfrom()，例如：
int main(void) {
struct sockaddr_in si_me, si_other;
int s, i, blen, slen = sizeof(si_other);
char buf[BUFLEN];
s = socket(AF_INET, SOCK_DGRAM, IPPROTO_UDP);
if (s == -1)
die("socket");
memset((char *) &si_me, 0, sizeof(si_me));
si_me.sin_family = AF_INET;
si_me.sin_port = htons(1234);
si_me.sin_addr.s_addr = htonl(192.168.1.1);
if (bind(s, (struct sockaddr*) &si_me, sizeof(si_me))==-1)
die("bind");
int blen = recvfrom(s, buf, sizeof(buf), 0, (struct sockaddr*) &si_other, &slen);
if (blen == -1)
diep("recvfrom()");
printf("Data: %.*s \nReceived from %s:%d\n\n", blen, buf, inet_ntoa(si_other.sin_addr), ntohs(si_other.sin_port));
//send answer back to the client
if (sendto(s, buf, blen, 0, (struct sockaddr*) &si_other, slen) == -1)
diep("sendto()");
close(s);
return 0;
}
