/ # 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)