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 several times but couldn't find proper way to get IP address from sock structure.

I believe this is a way to get IP from sock struct after server accept request from client. More specifically in c after server execute

csock = accept(ssock, (struct sockaddr *)&client_addr, &clen)

Thanks

Goz · Accepted Answer · 2016-02-01T11:03:30.103

60

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 );

edited Feb 01 '16 at 11:03

answered Jun 17 '10 at 10:53

Goz

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You forgot to pass the `str` buffer to `inet_ntop()`. And `sin_addr` is a struct - one has to use `sin_addr.s_addr`. Worth noting that IPv4 address is stored in network byte order and to see it as a hex number one would need to use `ntohl(pV4Addr->sin_addr.s_addr)`. – Dummy00001 Jun 17 '10 at 12:22
Points taken ... you also missed my not using a lowercase "in6_addr" ;) On the ntohl front I don't often bother as I can still do equality checks (provided both are in network order) and it would break the inet_ntop (wouldn't it?). – Goz Jun 17 '10 at 12:58
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This question is tagged C - you can't leave out the `struct` in types like `struct sockaddr_in *`. Also, the IPV4 method should use `struct in_addr` instead of `int` to store addresses, analagous to the IPV6 method you show. – caf Jun 18 '10 at 05:57

score 46 · Answer 2 · edited May 21 '14 at 15:45

46

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.

edited May 21 '14 at 15:45

Andrew Barber

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answered Apr 18 '13 at 08:02

Misha

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score 27 · Answer 3 · answered Jun 17 '10 at 10:54

27

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));

answered Jun 17 '10 at 10:54

SoapBox

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You should use inet_ntoa() instead of fiddling with the bits manually. – Remy Lebeau Jun 18 '10 at 01:15
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`inet_ntoa` is not thread-safe, although that might not be important for most cases where it's used. A safe alternative is `inet_ntop`. – jweyrich Apr 29 '13 at 05:13
@RemyLebeau Nice and simple. I like it. – James May 15 '17 at 21:14

How to get ip address from sock structure in c?

3 Answers3

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