GETHOSTBYNAME(3) BSD Library Functions Manual GETHOSTBYNAME(3)
NAME
gethostbyname, gethostbyname2, gethostbyaddr, gethostent, sethostent,
endhostent, herror, hstrerror -- get network host entry
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
##include <>
extern int herrno;
struct hostent *
gethostbyname(const char *name);
struct hostent *
gethostbyname2(const char *name, int af);
struct hostent *
gethostbyaddr(const char *addr, socklent len, int type);
struct hostent *
gethostent(void);
void
sethostent(int stayopen);
void
endhostent(void);
void
herror(const char *string);
const char *
hstrerror(int err);
DESCRIPTION
The gethostbyname(), gethostbyname2() and gethostbyaddr() functions each
return a pointer to an object with the following structure describing an
internet host referenced by name or by address, respectively. This
structure contains either the information obtained from the name server,
named(8), or broken-out fields from a line in /etc/hosts. If the local
name server is not running these routines do a lookup in /etc/hosts.
struct hostent {
char *hname; /* official name of host */
char **haliases; /* alias list */
int haddrtype; /* host address type */
int hlength; /* length of address */
char **haddrlist; /* list of addresses from name server */
};
#define haddr haddrlist[0] /* address, for backward compatibility */
The members of this structure are:
hname Official name of the host.
haliases A NUL-terminated array of alternate names for the host.
haddrtype The type of address being returned; usually AFINET.
hlength The length, in bytes, of the address.
haddrlist A NUL-terminated array of network addresses for the host.
Host addresses are returned in network byte order.
haddr The first address in haddrlist; this is for backward com-
patibility.
When using the nameserver, gethostbyname() and gethostbyname2() will
search for the named host in the current domain and its parents unless
the name ends in a dot. If the name contains no dot, and if the environ-
ment variable ``HOSTALIASES'' contains the name of an alias file, the
alias file will first be searched for an alias matching the input name.
See hostname(7) for the domain search procedure and the alias file for-
mat.
The gethostbyname2() function is an evolution of gethostbyname() which is
intended to allow lookups in address families other than AFINET, for
example AFINET6. Both of these address families are supported in the
Mac OS X implemention.
The sethostent() function may be used to request the use of a connected
TCP socket for queries. If the stayopen flag is non-zero, this sets the
option to send all queries to the name server using TCP and to retain the
connection after each call to gethostbyname(), gethostbyname2() or
gethostbyaddr(). Otherwise, queries are performed using UDP datagrams.
The endhostent() function closes the TCP connection.
The herror() function writes a message to the diagnostic output consist-
ing of the string parameter s, the constant string ": ", and a message
corresponding to the value of herrno.
The hstrerror() function returns a string which is the message text cor-
responding to the value of the err parameter.
FILES
/etc/hosts
/etc/host.conf
/etc/resolv.conf
DIAGNOSTICS
Error return status from gethostbyname(), gethostbyname2() and
gethostbyaddr() is indicated by return of a NUL pointer. The external
integer herrno may then be checked to see whether this is a temporary
failure or an invalid or unknown host. The routine herror() can be used
to print an error message describing the failure. If its argument string
is non-NUL, it is printed, followed by a colon and a space. The error
message is printed with a trailing newline.
The variable herrno can have the following values:
HOSTNOTFOUND No such host is known.
TRYAGAIN This is usually a temporary error and means that the
local server did not receive a response from an authori-
tative server. A retry at some later time may succeed.
NORECOVERY Some unexpected server failure was encountered. This is
a non-recoverable error.
NODATA The requested name is valid but does not have an IP
address; this is not a temporary error. This means that
the name is known to the name server but there is no
address associated with this name. Another type of
request to the name server using this domain name will
result in an answer; for example, a mail-forwarder may be
registered for this domain.
SEE ALSO
getaddrinfo(3), resolver(3), hosts(5), hostname(7), named(8)
CAVEAT
The gethostent() function is defined, and sethostent() and endhostent()
are redefined, when libc is built to use only the routines to lookup in
/etc/hosts and not the name server.
The gethostent() function reads the next line of /etc/hosts, opening the
file if necessary.
The sethostent() function opens and/or rewinds the file /etc/hosts. If
the stayopen argument is non-zero, the file will not be closed after each
call to gethostbyname(), gethostbyname2() or gethostbyaddr().
The endhostent() function closes the file.
HISTORY
The herror() function appeared in 4.3BSD. The endhostent(),
gethostbyaddr(), gethostbyname(), gethostent(), and sethostent() func-
tions appeared in 4.2BSD. The gethostbyname2() function first appeared
in BIND version 4.9.4.
BUGS
These functions use static data storage; if the data is needed for future
use, it should be copied before any subsequent calls overwrite it. Only
the Internet address format is currently understood.
BSD May 25, 1995 BSD
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