How to get ip address from sock structure in c?

Question

I\'m writing simple server/client and trying to get client IP address and save it on server side to decide which client should get into critical section. I googled it severa

Answer 1

Assuming client_addr is a struct sockaddr_in (which it usually is). You can get the IP address (as a 32-bit unsigned integer) from client_addr.sin_addr.s_addr.

You can convert it to a string this way:

printf("%d.%d.%d.%d\n",
  int(client.sin_addr.s_addr&0xFF),
  int((client.sin_addr.s_addr&0xFF00)>>8),
  int((client.sin_addr.s_addr&0xFF0000)>>16),
  int((client.sin_addr.s_addr&0xFF000000)>>24));

Answer 2

OK assuming you are using IPV4 then do the following:

struct sockaddr_in* pV4Addr = (struct sockaddr_in*)&client_addr;
struct in_addr ipAddr = pV4Addr->sin_addr;

If you then want the ip address as a string then do the following:

char str[INET_ADDRSTRLEN];
inet_ntop( AF_INET, &ipAddr, str, INET_ADDRSTRLEN );

IPV6 is pretty easy as well ...

struct sockaddr_in6* pV6Addr = (struct sockaddr_in6*)&client_addr;
struct in6_addr ipAddr       = pV6Addr->sin6_addr;

and getting a string is almost identical to IPV4

char str[INET6_ADDRSTRLEN];
inet_ntop( AF_INET6, &ipAddr, str, INET6_ADDRSTRLEN );

Answer 3

The easier and correct way for extracting IP address and port number would be:

printf("IP address is: %s\n", inet_ntoa(client_addr.sin_addr));
printf("port is: %d\n", (int) ntohs(client_addr.sin_port));

The SoapBox's accepted answer won't be correct for all architectures. See Big and Little Endian.