/ # cat test.c && ./test -v && strace ./test && ifconfig -a
#include <stdbool.h>
#include <stdio.h>

#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>

void print_ai( struct addrinfo *ai ) {

	unsigned family;
	char addrs[ INET6_ADDRSTRLEN ];
	unsigned port;
	struct sockaddr_in *sai;
	struct sockaddr_in6 *sai6;

	if ( ai->ai_addr ) {
		switch( ai->ai_addr->sa_family ) {
		case AF_INET:
			sai = ai->ai_addr;
			inet_ntop( AF_INET, & sai->sin_addr, addrs, sizeof( addrs ) );
			break;
		case AF_INET6:
			sai6 = ai->ai_addr;
			inet_ntop( AF_INET6, & sai6->sin6_addr, addrs, sizeof( addrs ) );
			break;
		default:
			break;
		}
	}
	
	printf(
		"struct addrinfo {" "\n"
		"   ai_flags:        %x" "\n"
		"   ai_family:       %u" "\n"
		"   ai_socktype:     %u" "\n"
		"   ai_protocol:     %u" "\n"
		"   ai_addrlen:      %u" "\n"
		"   ai_addr:           " "\n"
		"      family:       %u" "\n"
		"      addr:         %s" "\n"
		"      port:         %u" "\n"
		"   ai_canonname:    %s" "\n"
		"   ai_next:         %p" "\n"
		"}                     " "\n",
		ai->ai_flags,
		ai->ai_family,
		ai->ai_socktype,
		ai->ai_protocol,
		ai->ai_addrlen,
		NULL == ai->ai_addr ? "??" : ai->ai_addr->sa_family,
		NULL == ai->ai_addr ? "??" : addrs,
		NULL == ai->ai_addr ? "??" : port,
		ai->ai_canonname ? ai->ai_canonname : "(null)",
		ai->ai_next
	);
}

int main( int argc, char *argv[] ) {
	int r;

	struct addrinfo hints = {
		.ai_family = PF_UNSPEC,
		.ai_socktype = SOCK_STREAM,
		.ai_flags = AI_V4MAPPED | AI_ADDRCONFIG,
	};
	struct addrinfo *res;
	struct addrinfo *it;

	bool verbose = argc > 1;

	r = getaddrinfo( "localhost", NULL, & hints, & res );
	if ( 0 != r ) {
		perror( "getaddrinfo" );
		return r;
	}

	if ( verbose ) {
		for( it = res; NULL != it; it = it->ai_next ) {
			print_ai( it );
		}
	}

	freeaddrinfo( res );

	return r;
}

struct addrinfo {
   ai_flags:        0
   ai_family:       2
   ai_socktype:     1
   ai_protocol:     6
   ai_addrlen:      16
   ai_addr:           
      family:       2
      addr:         127.0.0.1
      port:         0
   ai_canonname:    localhost
   ai_next:         0x55d919dce0d0
}                     
struct addrinfo {
   ai_flags:        0
   ai_family:       10
   ai_socktype:     1
   ai_protocol:     6
   ai_addrlen:      28
   ai_addr:           
      family:       10
      addr:         ::1
      port:         0
   ai_canonname:    localhost
   ai_next:         0
}                     
execve("./test", ["./test"], 0x7ffcb6904280 /* 6 vars */) = 0
arch_prctl(ARCH_SET_FS, 0x7fc81f0cdb88) = 0
set_tid_address(0x7fc81f0cdbc0)         = 101
mprotect(0x7fc81f0ca000, 4096, PROT_READ) = 0
mprotect(0x55eccc5f2000, 4096, PROT_READ) = 0
open("/etc/hosts", O_RDONLY|O_CLOEXEC)  = 3
fcntl(3, F_SETFD, FD_CLOEXEC)           = 0
readv(3, [{iov_base="", iov_len=0}, {iov_base="127.0.0.1\tlocalhost\n::1\tlocalhos"..., iov_len=1024}], 2) = 174
readv(3, [{iov_base="", iov_len=0}, {iov_base="", iov_len=1024}], 2) = 0
close(3)                                = 0
socket(AF_INET6, SOCK_DGRAM|SOCK_CLOEXEC, IPPROTO_UDP) = 3
connect(3, {sa_family=AF_INET6, sin6_port=htons(65535), inet_pton(AF_INET6, "::ffff:127.0.0.1", &sin6_addr), sin6_flowinfo=htonl(0), sin6_scope_id=0}, 28) = 0
getsockname(3, {sa_family=AF_INET6, sin6_port=htons(53878), inet_pton(AF_INET6, "::ffff:127.0.0.1", &sin6_addr), sin6_flowinfo=htonl(0), sin6_scope_id=0}, [28]) = 0
close(3)                                = 0
socket(AF_INET6, SOCK_DGRAM|SOCK_CLOEXEC, IPPROTO_UDP) = 3
connect(3, {sa_family=AF_INET6, sin6_port=htons(65535), inet_pton(AF_INET6, "::1", &sin6_addr), sin6_flowinfo=htonl(0), sin6_scope_id=0}, 28) = -1 EADDRNOTAVAIL (Address not available)
close(3)                                = 0
exit_group(0)                           = ?
+++ exited with 0 +++
eth0      Link encap:Ethernet  HWaddr 02:42:AC:11:00:03  
          inet addr:172.17.0.3  Bcast:172.17.255.255  Mask:255.255.0.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:26909 errors:0 dropped:0 overruns:0 frame:0
          TX packets:13292 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:39372973 (37.5 MiB)  TX bytes:720894 (703.9 KiB)

ip6tnl0   Link encap:UNSPEC  HWaddr 00-00-00-00-00-00-00-00-00-00-00-00-00-00-00-00  
          NOARP  MTU:1452  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1 
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

lo        Link encap:Local Loopback  
          inet addr:127.0.0.1  Mask:255.0.0.0
          UP LOOPBACK RUNNING  MTU:65536  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1 
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)

tunl0     Link encap:UNSPEC  HWaddr 00-00-00-00-00-00-87-AF-00-00-00-00-00-00-00-00  
          NOARP  MTU:1480  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1 
          RX bytes:0 (0.0 B)  TX bytes:0 (0.0 B)