C语言 如何从 unix c 中的 struct addrinfo 获取端口号
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How to get the port number from struct addrinfo in unix c
提问by sfactor
I need to send some data to a remote server via UDP in a particular port and get receive a response from it. However, it is blocking and I do not get any response. I need to check if the addrinfo value that I get from the getaddrinfo(SERVER_NAME, port, &hints, &servinfo)is correct or not.
我需要通过特定端口中的 UDP 将一些数据发送到远程服务器并从它接收响应。但是，它正在阻塞，我没有得到任何响应。我需要检查我从 中获得的 addrinfo 值getaddrinfo(SERVER_NAME, port, &hints, &servinfo)是否正确。
How do I get the port number from this data structure?
如何从这个数据结构中获取端口号？
I know inet_ntop(p->ai_family, get_in_addr((struct sockaddr *)p->ai_addr), s, sizeof s)gives me server IP address. (I am using the method in Beej's guide.)
我知道inet_ntop(p->ai_family, get_in_addr((struct sockaddr *)p->ai_addr), s, sizeof s)给了我服务器 IP 地址。（我正在使用 Beej 指南中的方法。）
回答by David Gelhar
You do something similar to what Beej's get_in_addr function does:
你做一些类似于 Beej 的 get_in_addr 函数所做的事情：
// get port, IPv4 or IPv6:
in_port_t get_in_port(struct sockaddr *sa)
{
if (sa->sa_family == AF_INET)
return (((struct sockaddr_in*)sa)->sin_port);
return (((struct sockaddr_in6*)sa)->sin6_port);
}
Also beware of the #1 pitfall dealing with port numbers in sockaddr_in(or sockaddr_in6) structures: port numbers are always stored in network byte order.
还要注意在sockaddr_in（或sockaddr_in6）结构中处理端口号的#1 陷阱：端口号总是以网络字节顺序存储。
That means, for example, that if you print out the result of the get_in_port()call above, you need to throw in a ntohs():
这意味着，例如，如果你打印出get_in_port()上面调用的结果，你需要抛出一个ntohs()：
printf("port is %d\n", ntohs(get_in_port((struct sockaddr *)p->ai_addr)));
