1GETIPNODEBYNAME(3)       BSD Library Functions Manual       GETIPNODEBYNAME(3)
2

NAME

4     getipnodebyname, getipnodebyaddr — get network host entry
5     freehostent — free network host entry
6

SYNOPSIS

8     #include <netdb.h>
9
10     struct hostent *
11     getipnodebyname(const char *name, int af, int flags, int *error);
12
13     struct hostent *
14     getipnodebyaddr(const void *addr, size_t len, int af, int *error);
15
16     void
17     freehostent(struct hostent *he);
18

DESCRIPTION

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, named(8), or
24     broken-out fields from a line in /etc/hosts.  If the local name server is
25     not running, these routines do a lookup in /etc/hosts.
26
27           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
35           #define h_addr  h_addr_list[0]  /* address, for backward compatibility */
36
37     The members of this structure are:
38
39     h_name       Official name of the host.
40
41     h_aliases    A zero-terminated array of alternate names for the host.
42
43     h_addrtype   The type of address being returned.
44
45     h_length     The length, in bytes, of the address.
46
47     h_addr_list  A zero-terminated array of network addresses for the host.
48                  Host addresses are returned in network byte order.
49
50     h_addr       The first address in h_addr_list; this is for backward com‐
51                  patibility.
52
53     This structure should be freed after use by calling freehostent().
54
55     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
63     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
67     There are three flags that can be set
68
69     AI_V4MAPPED    Return IPv4 addresses if no IPv6 addresses are found.
70                    This flag is ignored unless af is AF_INET6.
71
72     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
76     AI_ADDRCONFIG  Only return addresses of a given type if the system has an
77                    active interface with that type.
78
79     Also AI_DEFAULT is defined to be (AI_V4MAPPED|AI_ADDRCONFIG).
80
81     Getipnodebyaddr() will lookup IPv4 mapped and compatible addresses in the
82     IPv4 name space and IPv6 name space
83
84     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

ENVIRONMENT

90     HOSTALIASES    Name of file containing (host alias, full hostname) pairs.
91

FILES

93     /etc/hosts     See hosts(5).
94

DIAGNOSTICS

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
101           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(3).
104
105           HOST_NOT_FOUND    No such host is known.
106
107           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
112           NO_RECOVERY       Some unexpected server failure was encountered.
113                             This is a non-recoverable error, as one might
114                             expect.
115
116           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

SEE ALSO

126     hosts(5), hostname(7), named(8), resolver(3), resolver(5),
127     gethostbyname(3), RFC2553.
128
1294th Berkeley Distribution     September 17, 1999     4th Berkeley Distribution
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