1GETIPNODEBYNAME(3) BSD Library Functions Manual GETIPNODEBYNAME(3)
2
4 getipnodebyname, getipnodebyaddr — get network host entry
5 freehostent — free network host entry
6
8 #include <netdb.h>
9 struct hostent *
11 getipnodebyname(const char *name, int af, int flags, int *error);
12 struct hostent *
14 getipnodebyaddr(const void *addr, size_t len, int af, int *error);
15 void
17 freehostent(struct hostent *he);
18
20 Getipnodebyname(), and getipnodebyaddr() each return a pointer to a
21 hostent structure (see below) describing an internet host referenced by
22 name or by address, as the function names indicate. This structure con‐
23 tains either the information obtained from the name server, or broken-out
24 fields from a line in /etc/hosts. If the local name server is not run‐
25 ning, these routines do a lookup in /etc/hosts.
26 struct hostent {
28 char *h_name; /* official name of host */
29 char **h_aliases; /* alias list */
30 int h_addrtype; /* host address type */
31 int h_length; /* length of address */
32 char **h_addr_list; /* list of addresses from name server */
33 };
34 #define h_addr h_addr_list[0] /* address, for backward compatibility */
36 The members of this structure are:
38 h_name Official name of the host.
40 h_aliases A zero-terminated array of alternate names for the host.
42 h_addrtype The type of address being returned.
44 h_length The length, in bytes, of the address.
46 h_addr_list A zero-terminated array of network addresses for the host.
48 Host addresses are returned in network byte order.
49 h_addr The first address in h_addr_list; this is for backward com‐
51 patibility.
52 This structure should be freed after use by calling freehostent().
54 When using the nameserver, getiphostbyaddr() will search for the named
56 host in each parent domain given in the “search” directive of
57 resolv.conf(5) unless the name contains a dot (“.”). If the name con‐
58 tains no dot, and if the environment variable HOSTALIASES contains the
59 name of an alias file, the alias file will first be searched for an alias
60 matching the input name. See hostname(7) for the domain search procedure
61 and the alias file format.
62 Getiphostbyaddr() can be told to look for IPv4 addresses, IPv6 addresses
64 or both IPv4 and IPv6. If IPv4 addresses only are to be looked up then
65 af should be set to AF_INET, otherwise it should be set to AF_INET6.
66 There are three flags that can be set
68 AI_V4MAPPED Return IPv4 addresses if no IPv6 addresses are found.
70 This flag is ignored unless af is AF_INET6.
71 AI_ALL Return IPv4 addresses as well IPv6 addresses if
73 AI_V4MAPPED is set. This flag is ignored unless af is
74 AF_INET6.
75 AI_ADDRCONFIG Only return addresses of a given type if the system has an
77 active interface with that type.
78 Also AI_DEFAULT is defined to be (AI_V4MAPPED|AI_ADDRCONFIG).
80 Getipnodebyaddr() will lookup IPv4 mapped and compatible addresses in the
82 IPv4 name space and IPv6 name space
83 Freehostent() frees the hostent structure allocated be getipnodebyname()
85 and getipnodebyaddr(). The structures returned by gethostbyname(),
86 gethostbyname2(), gethostbyaddr() and gethostent() should not be passed
87 to freehostent() as they are pointers to static areas.
88
90 HOSTALIASES Name of file containing (host alias, full hostname) pairs.
91
93 /etc/hosts See hosts(5).
94
96 Error return status from getipnodebyname() and getipnodebyaddr() is indi‐
97 cated by return of a null pointer. In this case error may then be
98 checked to see whether this is a temporary failure or an invalid or
99 unknown host. errno can have the following values:
100 NETDB_INTERNAL This indicates an internal error in the library,
102 unrelated to the network or name service. errno
103 will be valid in this case; see perror.
104 HOST_NOT_FOUND No such host is known.
106 TRY_AGAIN This is usually a temporary error and means that
108 the local server did not receive a response from
109 an authoritative server. A retry at some later
110 time may succeed.
111 NO_RECOVERY Some unexpected server failure was encountered.
113 This is a non-recoverable error, as one might
114 expect.
115 NO_ADDRESS The requested name is valid but does not have an
117 IP address; this is not a temporary error. This
118 means that the name is known to the name server
119 but there is no address associated with this
120 name. Another type of request to the name server
121 using this domain name will result in an answer;
122 for example, a mail-forwarder may be registered
123 for this domain.
124
126 hosts(5), hostname(7), resolver(3), resolver(5), gethostbyname(3),
127 RFC2553.
1284th Berkeley Distribution September 17, 1999 4th Berkeley Distribution