Getting IPV4 address from a sockaddr structure
Just cast the entire sockaddr
structure to a sockaddr_in. Then you can use:
char *ip = inet_ntoa(their_addr.sin_addr)
To retrieve the standard ip representation.
inet_ntoa()
works for IPv4; inet_ntop()
works for both IPv4 and IPv6.
Given an input struct sockaddr *res
, here are two snippets of code (tested on macOS):
Using inet_ntoa()
#include <arpa/inet.h>struct sockaddr_in *addr_in = (struct sockaddr_in *)res;char *s = inet_ntoa(addr_in->sin_addr);printf("IP address: %s\n", s);
Using inet_ntop()
#include <arpa/inet.h>#include <stdlib.h>// obviously INET6_ADDRSTRLEN is expected to be larger// than INET_ADDRSTRLEN, but this may be required in case// if for some unexpected reason IPv6 is not supported, and// INET6_ADDRSTRLEN is defined as 0// but this is not very likely and I am aware of no cases of// this in practice (editor)char s[INET6_ADDRSTRLEN > INET_ADDRSTRLEN ? INET6_ADDRSTRLEN : INET_ADDRSTRLEN] = '\0';switch(res->sa_family) { case AF_INET: { struct sockaddr_in *addr_in = (struct sockaddr_in *)res; ////char s[INET_ADDRSTRLEN] = '\0'; // this is large enough to include terminating null inet_ntop(AF_INET, &(addr_in->sin_addr), s, INET_ADDRSTRLEN); break; } case AF_INET6: { struct sockaddr_in6 *addr_in6 = (struct sockaddr_in6 *)res; ////char s[INET6_ADDRSTRLEN] = '\0'; // not sure if large enough to include terminating null? inet_ntop(AF_INET6, &(addr_in6->sin6_addr), s, INET6_ADDRSTRLEN); break; } default: break;}printf("IP address: %s\n", s);
Emil's answer is correct, but it's my understanding that inet_ntoa
is deprecated and that instead you should use inet_ntop
. If you are using IPv4, cast your struct sockaddr
to sockaddr_in
. Your code will look something like this:
struct addrinfo *res; // populated elsewhere in your codestruct sockaddr_in *ipv4 = (struct sockaddr_in *)res->ai_addr;char ipAddress[INET_ADDRSTRLEN];inet_ntop(AF_INET, &(ipv4->sin_addr), ipAddress, INET_ADDRSTRLEN);printf("The IP address is: %s\n", ipAddress);
Take a look at this great resource for more explanation, including how to do this for IPv6 addresses.