How to get IP address from sockaddr

Question

I want to try and get the ip address of a client after calling accept. This is what I have so far, but I just end up getting some long number that is clearly not an ip addr

Answer 1

While these are good answers, they broke my compile with -pedantic -std=c99 -Werror.

From man 7 socket

To allow any type of socket address to be passed to interfaces in the sockets API, the type struct sockaddr is defined. The purpose of this type is purely to allow casting of domain-specific socket address types to a "generic" type, so as to avoid compiler warnings about type mismatches in calls to the sockets API.

To get all the relevant data in this page, from glibc-2.17 (RHEL7) I see

/* Structure describing a generic socket address.  */
struct sockaddr
  {
    __SOCKADDR_COMMON (sa_);    /* Common data: address family and length.  */
    char sa_data[14];       /* Address data.  */
  };

where SOCKADDR_COMMON is a uint16_t. So total size is 16B.

IP (internet protocol) Domain specific, from man 7 ip:

struct sockaddr_in {
    sa_family_t    sin_family; /* address family: AF_INET */
    in_port_t      sin_port;   /* port in network byte order */
    struct in_addr sin_addr;   /* internet address */
};

/* Internet address. */
struct in_addr {
    uint32_t       s_addr;     /* address in network byte order */
};

First try

inet_ntoa( ((struct sockaddr_in) peer_addr).sin_addr )

Problem

error: conversion to non-scalar type requested

Second try

 inet_ntoa( ((struct sockaddr_in *) &peer_addr)->sin_addr ) ));

Problem

error: dereferencing type-punned pointer might break strict-aliasing rules [-Werror=strict-aliasing]

Thrid try: inet_pton, more modern anyways, thread safe, takes void*

char peer_addr_str[ INET_ADDRSTRLEN ];
inet_ntop( AF_INET, &peer_addr, peer_addr_str, INET_ADDRSTRLEN );

ok, works. Human readable decimal-and-dots string is in peer_addr_str.