1GETHOSTBYNAME(3) Library Functions Manual GETHOSTBYNAME(3)
2
6 gethostbyname, gethostbyaddr, gethostent, sethostent, endhostent, her‐
7 ror - get network host entry
8
10 #include <netdb.h>
11 extern int h_errno;
13 struct hostent *gethostbyname(name)
15 char *name;
16 struct hostent *gethostbyaddr(addr, len, type)
18 char *addr; int len, type;
19 struct hostent *gethostent()
21 sethostent(stayopen)
23 int stayopen;
24 endhostent()
26 herror(string)
28 char *string;
29
31 Gethostbyname and gethostbyaddr each return a pointer to an object with
32 the following structure describing an internet host referenced by name
33 or by address, respectively. This structure contains either the infor‐
34 mation obtained from the name server, named(8), or broken-out fields
35 from a line in /etc/hosts. If the local name server is not running
36 these routines do a lookup in /etc/hosts.
37 struct hostent {
39 char *h_name; /* official name of host */
40 char **h_aliases; /* alias list */
41 int h_addrtype; /* host address type */
42 int h_length; /* length of address */
43 char **h_addr_list; /* list of addresses from name server */
44 };
45 #define h_addr h_addr_list[0] /* address, for backward compatibility */
46 The members of this structure are:
48 h_name Official name of the host.
50 h_aliases A zero terminated array of alternate names for the host.
52 h_addrtype The type of address being returned; currently always
54 AF_INET.
55 h_length The length, in bytes, of the address.
57 h_addr_list A zero terminated array of network addresses for the host.
59 Host addresses are returned in network byte order.
60 h_addr The first address in h_addr_list; this is for backward
62 compatiblity.
63 When using the nameserver, gethostbyname will search for the named host
65 in the current domain and its parents unless the name ends in a dot.
66 If the name contains no dot, and if the environment variable ``HOSTAL‐
67 IASES'' contains the name of an alias file, the alias file will first
68 be searched for an alias matching the input name. See hostname(7) for
69 the domain search procedure and the alias file format.
70 Sethostent may be used to request the use of a connected TCP socket for
72 queries. If the stayopen flag is non-zero, this sets the option to
73 send all queries to the name server using TCP and to retain the connec‐
74 tion after each call to gethostbyname or gethostbyaddr. Otherwise,
75 queries are performed using UDP datagrams.
76 Endhostent closes the TCP connection.
78
80 Error return status from gethostbyname and gethostbyaddr is indicated
81 by return of a null pointer. The external integer h_errno may then be
82 checked to see whether this is a temporary failure or an invalid or
83 unknown host. The routine herror can be used to print an error message
84 describing the failure. If its argument string is non-NULL, it is
85 printed, followed by a colon and a space. The error message is printed
86 with a trailing newline.
87 h_errno can have the following values:
89 HOST_NOT_FOUND No such host is known.
91 TRY_AGAIN This is usually a temporary error and means that
93 the local server did not receive a response from
94 an authoritative server. A retry at some later
95 time may succeed.
96 NO_RECOVERY Some unexpected server failure was encountered.
98 This is a non-recoverable error.
99 NO_DATA The requested name is valid but does not have an
101 IP address; this is not a temporary error. This
102 means that the name is known to the name server
103 but there is no address associated with this
104 name. Another type of request to the name
105 server using this domain name will result in an
106 answer; for example, a mail-forwarder may be
107 registered for this domain.
108
110 /etc/hosts
111
113 resolver(3), hosts(5), hostname(7), named(8)
114
116 Gethostent is defined, and sethostent and endhostent are redefined,
117 when libc is built to use only the routines to lookup in /etc/hosts and
118 not the name server.
119 Gethostent reads the next line of /etc/hosts, opening the file if nec‐
121 essary.
122 Sethostent is redefined to open and rewind the file. If the stayopen
124 argument is non-zero, the hosts data base will not be closed after each
125 call to gethostbyname or gethostbyaddr. Endhostent is redefined to
126 close the file.
127
129 All information is contained in a static area so it must be copied if
130 it is to be saved. Only the Internet address format is currently
131 understood.
1324.2 Berkeley Distribution October 30, 1996 GETHOSTBYNAME(3)