ggreco
April 24th, 2009, 04:51 PM
I've the following code that works on every linux variant I tried (including various debian servers) except with ubuntu (tried with 8.04 and 9.04), what's wrong with it:
in_addr_t get_local_address()
{
char ac[80];
struct hostent *phe;
if (gethostname(ac, sizeof(ac)) == SOCKET_ERROR)
return INADDR_NONE;
std::cerr << "Hostname: <" << ac << ">\n";
if ((phe = gethostbyname(ac) )== 0)
return INADDR_NONE;
std::cerr << "Available addresses:\n";
for (int i = 0; phe->h_addr_list[i] != 0; ++i) {
in_addr_t addr;
memcpy(&addr, phe->h_addr_list[i], sizeof(addr));
struct in_addr a;
a.s_addr = addr;
std::cerr << "Address " << i << " - " << inet_ntoa(a) << '\n';
// avoid local addresses
if (((unsigned char *)&addr)[0] != 127)
return addr;
}
return INADDR_NONE;
}
ifconfig returns the correct address (192.168.8.40) that I'd like to grab with the previous function:
eth0 Link encap:Ethernet HWaddr 00:13:49:25:73:b4
inet addr:192.168.8.40 Bcast:192.168.8.255 Mask:255.255.255.0
inet6 addr: fe80::213:49ff:fe25:73b4/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:302772 errors:0 dropped:0 overruns:0 frame:0
TX packets:234818 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:171691551 (171.6 MB) TX bytes:58548246 (58.5 MB)
Interrupt:18 Base address:0xf600
eth1 Link encap:Ethernet HWaddr 00:1c:25:4e:17:54
UP BROADCAST MULTICAST MTU:1500 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:1000
RX bytes:0 (0.0 B) TX bytes:0 (0.0 B)
Interrupt:19 Base address:0xdead
lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
inet6 addr: ::1/128 Scope:Host
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:8338 errors:0 dropped:0 overruns:0 frame:0
TX packets:8338 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:1498751 (1.4 MB) TX bytes:1498751 (1.4 MB)
I suppose the problem is that /etc/hosts contains only the local address reference for "nevada" (the hostname returned also by gethostname()) and that gethostbyname() doesn't check the DNS since it finds an answer in /etc/hosts.
127.0.0.1 localhost
127.0.1.1 nevada
# The following lines are desirable for IPv6 capable hosts
::1 ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
ff02::3 ip6-allhosts
The problem is that this behaviour is the default one with a "fresh install", so I cannot rely on the fact users has a "correct" /etc/hosts...
There is another way to get the current ip address used for outbound TCP/IP communications without doing ugly things like grepping ifconfig or route command output?
in_addr_t get_local_address()
{
char ac[80];
struct hostent *phe;
if (gethostname(ac, sizeof(ac)) == SOCKET_ERROR)
return INADDR_NONE;
std::cerr << "Hostname: <" << ac << ">\n";
if ((phe = gethostbyname(ac) )== 0)
return INADDR_NONE;
std::cerr << "Available addresses:\n";
for (int i = 0; phe->h_addr_list[i] != 0; ++i) {
in_addr_t addr;
memcpy(&addr, phe->h_addr_list[i], sizeof(addr));
struct in_addr a;
a.s_addr = addr;
std::cerr << "Address " << i << " - " << inet_ntoa(a) << '\n';
// avoid local addresses
if (((unsigned char *)&addr)[0] != 127)
return addr;
}
return INADDR_NONE;
}
ifconfig returns the correct address (192.168.8.40) that I'd like to grab with the previous function:
eth0 Link encap:Ethernet HWaddr 00:13:49:25:73:b4
inet addr:192.168.8.40 Bcast:192.168.8.255 Mask:255.255.255.0
inet6 addr: fe80::213:49ff:fe25:73b4/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:302772 errors:0 dropped:0 overruns:0 frame:0
TX packets:234818 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:1000
RX bytes:171691551 (171.6 MB) TX bytes:58548246 (58.5 MB)
Interrupt:18 Base address:0xf600
eth1 Link encap:Ethernet HWaddr 00:1c:25:4e:17:54
UP BROADCAST MULTICAST MTU:1500 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:1000
RX bytes:0 (0.0 B) TX bytes:0 (0.0 B)
Interrupt:19 Base address:0xdead
lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
inet6 addr: ::1/128 Scope:Host
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:8338 errors:0 dropped:0 overruns:0 frame:0
TX packets:8338 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:0
RX bytes:1498751 (1.4 MB) TX bytes:1498751 (1.4 MB)
I suppose the problem is that /etc/hosts contains only the local address reference for "nevada" (the hostname returned also by gethostname()) and that gethostbyname() doesn't check the DNS since it finds an answer in /etc/hosts.
127.0.0.1 localhost
127.0.1.1 nevada
# The following lines are desirable for IPv6 capable hosts
::1 ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
ff02::3 ip6-allhosts
The problem is that this behaviour is the default one with a "fresh install", so I cannot rely on the fact users has a "correct" /etc/hosts...
There is another way to get the current ip address used for outbound TCP/IP communications without doing ugly things like grepping ifconfig or route command output?