C++ 简单的UDP套接字代码，发送和接收消息
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Simple UDP socket code, sending and receiving messages
提问by forever_fighting_21
I am just learning UDP sockets and this is my first code involving it. I have two programs which send and receive messages back and forth. My question is it seems I have to declare which IP address I am sending/receiving from multiple times throughout the code as it changes but I feel there is a better way to do this without changing the inet_addr manually within the codes. From my reading it looks like sendto and recvfrom may be able to help but I am unsure how to use them in this context. If anyone could show me how to fix my simple problem I would greatly appreciate it! Thanks
我只是在学习 UDP 套接字，这是我第一个涉及它的代码。我有两个程序来回发送和接收消息。我的问题是似乎我必须在整个代码中多次声明我发送/接收的 IP 地址，因为它发生了变化，但我觉得有更好的方法来做到这一点，而无需在代码中手动更改 inet_addr。从我的阅读来看， sendto 和 recvfrom 可能会有所帮助，但我不确定如何在这种情况下使用它们。如果有人能告诉我如何解决我的简单问题，我将不胜感激！谢谢
CODE 1: Send then Receive
代码 1：发送然后接收
int main(int argc, char *argv[])
{
//initialize socket and structure
int socket_info;
struct sockaddr_in server;
char message[100];
char incoming_message[100];
printf("Input Message: ");
fgets(message, 100, stdin);
//create socket
socket_info = socket(AF_INET, SOCK_DGRAM, 0);
if (socket_info == -1) {
printf("Could not create socket");
}
//assign local values
server.sin_addr.s_addr = inet_addr("172.21.8.178");
server.sin_family = AF_INET;
server.sin_port = htons( 1100 );
//binds connection
if (bind(socket_info, (struct sockaddr *)&server, sizeof(server)) < 0) {
perror("Connection error");
return 1;
}
puts("Bind");
//assign new value to connect to
server.sin_addr.s_addr = inet_addr("172.21.8.179");
//checks connection
if (connect(socket_info, (struct sockaddr *)&server, sizeof(server)) < 0) {
perror("Connection error");
return 1;
}
puts("Connected");
//sends message
if(send(socket_info, message, strlen(message), 0) <0) {
perror("Send failed");
return 1;
}
puts("Message Sent");
//receives message back
if(recv(socket_info, incoming_message, sizeof(incoming_message), 0) <0) {
puts("Received failed");
return 1;
}
puts("Message received");
puts(incoming_message);
close(socket_info);
}
CODE 2: Receive then Send
代码 2：接收然后发送
int main(int argc, char *argv[])
{
//initialize socket and structure
int socket_info;
struct sockaddr_in server;
char incoming_message[100];
//create socket
socket_info = socket(AF_INET, SOCK_DGRAM, 0);
if (socket_info == -1) {
printf("Could not create socket");
}
//assign values
server.sin_addr.s_addr = inet_addr("172.21.8.179");
server.sin_family = AF_INET;
server.sin_port = htons( 1100 );
//checks connection
if (bind(socket_info, (struct sockaddr *)&server, sizeof(server)) < 0) {
perror("Connection error");
return 1;
}
puts("Bind");
//Receive an incoming message
if( recv(socket_info, incoming_message, sizeof(incoming_message), 0) < 0) {
puts("Received failed");
return 1;
}
puts("Message received");
puts(incoming_message);
server.sin_addr.s_addr = inet_addr("172.21.8.178");
if (connect(socket_info, (struct sockaddr *)&server, sizeof(server)) < 0) {
perror("Connection error");
return 1;
}
puts("Connected");
//Sends message back
char message[100];
printf("Input Message: ");
fgets(message, 100, stdin);
if(send(socket_info, message, strlen(message), 0) <0) {
perror("Send failed");
return 1;
}
puts("Message Sent");
close(socket_info);
}
回答by slangley
If you use the function recvfrom()
如果您使用函数 recvfrom()
ssize_t recvfrom(int sockfd, void *buf, size_t len, int flags,
struct sockaddr *src_addr, socklen_t *addrlen);
What this function does is it fills a structure of sockaddr with the IP and port information of the packet that it has just received. For example, if your code that sends first then receives sends a packet to the receiver, the receiver should be able to fill the structure values of sin_addr and sin_port with the correct values. You can then make a call of sendto() with this information in order to send it to the correct machine.
这个函数的作用是用它刚刚收到的数据包的IP和端口信息填充sockaddr的结构。例如，如果先发送后接收的代码向接收器发送了一个数据包，则接收器应该能够用正确的值填充 sin_addr 和 sin_port 的结构值。然后，您可以使用此信息调用 sendto() 以将其发送到正确的机器。
Here's the man pages for these functions:
以下是这些功能的手册页：
https://linux.die.net/man/2/recvfrom
https://linux.die.net/man/2/recvfrom
回答by Aditya Kothari
Try using this:
尝试使用这个：
inet_pton(AF_INET, "127.0.0.1", &serv_addr.sin_addr)
127.0.0.1 is the loopback IP. The address is used to establish an IP connection to the same machine, which seems to be your case.
127.0.0.1 是环回 IP。该地址用于建立到同一台机器的 IP 连接，这似乎是您的情况。
A detailed way to solve the problem can be found here
可以在这里找到解决问题的详细方法
