HP 3000 Manuals HP 3000 Manuals
GETHOSTENT
C Interface
#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
extern int h_errno;
struct hostent *gethostent()
struct hostent *gethostbyname(name)
char *name;
struct hostent *gethostbyaddr(addr, len, type)
char *addr;
int len, type;
sethostent(stayopen)
int stayopen;
endhostent()
Description
The gethostent, gethostbyname, and gethostbyaddr subroutines return a
pointer to a structure defined as follows in netdb.h:
struct hostent {
char *h_name; /* official name of host */
char **h_aliases; /* alias list */
int h_addrtype; /* address type */
int h_length; /* length of address */
char **h_addr_list; /* list of addresses from name server */
};
#define h_addr h_addr_list[0] /* address for backward */
/* compatibility */
The members of this structure are as follows:
h_name Official name of the host.
h_aliases A null-terminated array of alternate names for the
host.
h_addrtype The type of address being returned; currently
always AF_INET.
h_length The length, in bytes, of the address.
h_addr_list A null-terminated array of network addresses for
the host.
h_addr The first address in h_addr_list; this is for
compatibility with previous HP-UX implementations,
where a struct hostent contains only one network
address per host.
If the local system is configured to use the name server, then:
* The gethostent subroutine always returns a null pointer.
* The sethostent subroutine, if the stayopen flag is non-zero,
requests the use of a connected stream socket for queries to the
name server. The connection is retained after each call to
gethostbyname or gethostbyaddr.
* The endhostent subroutine closes the stream socket connection.
The gethostbyname and gethostbyaddr subroutines each retrieve host
information from the name server through the resolver. Names are matched
in a case-insensitive manner; for example, berkeley.edu, Berkeley.EDU,
and BERKELEY.EDU would all match the entry for berkeley.edu.
The resolver reads the configuration file RESLVCNF.NET.SYS to get the
default domain name and the Internet address of the initial hosts running
the name server. If the environment variable LOCALDOMAIN is set by the
user, that name is used as the default domain (overriding any other
default). If the name server Internet addresses are not listed in the
configuration file, the resolver aborts and the hosts file is tried (see
below). If there are errors in the configuration file, they are silently
ignored.
If the local system is not using the name server, then:
* The gethostent subroutine reads the next line of HOSTS.NET.SYS,
opening the file if necessary.
* The sethostent subroutine opens and rewinds the file. If the
stayopen flag is non-zero, the host database is not closed after
each call to gethostent (either directly or indirectly through one
of the other gethost calls).
* The endhostent subroutine closes the file.
* The gethostbyname subroutine sequentially searches from the
beginning of the file until a host name (among either the official
names or the aliases) matching its parameter name is found, or
until EOF is encountered. Names are matched in a case-insensitive
manner; for example, berkeley.edu, Berkeley.EDU, and BERKELEY.EDU
would all match the entry for berkeley.edu.
* The gethostbyaddr subroutine sequentially searches from the
beginning of the file until an Internet address matching its
parameter addr is found, or until EOF is encountered.
In calls to gethostbyaddr, the parameter addr must point to an internet
address in network order (refer to the inet section) and the addr
parameter must be 4-byte aligned, or an escape is generated. The
parameter len must be the number of bytes in an Internet address, that
is, sizeof (struct in_addr). The parameter type must be the constant
AF_INET.
Return Value
If successful, gethostbyname, gethostbyaddr, and gethostent return a
pointer to the requested hostent struct. The gethostbyname and
gethostbyaddr subroutines return NULL if their host or addr parameters,
respectively, cannot be found in the database. If hosts.net.sys is being
used, they also return NULL if they are unable to open hosts.net.sys.
The gethostbyaddr subroutine also returns NULL if either its addr or len
parameter is invalid. The gethostent subroutine always returns NULL if
the name server is being used.
If the name server is being used and gethostbyname or gethostbyaddr
returns a NULL pointer, the external integer h_errno contains one of the
following values:
[HOST_NOT_FOUND] No such host is known.
[TRY_AGAIN] This is usually a temporary error and means
that the local server did not receive a
response from an authoritative server. A retry
at some time later may succeed.
[NO_RECOVERY] This is a non-recoverable error.
[NO_ADDRESS] The requested name is valid but has no IP
address; this is not a temporary error. This
means that another type of request to the name
server results in an answer.
If the name server is not being used, the value of h_errno may not be
meaningful.
Restrictions
All information is contained in a static area, so it must be copied if it
is to be saved. Only the Internet address format is currently
understood.
MPE/iX Specific
The names of the hosts file and resolver configuration file on MPE/iX are
HOSTS.NET.SYS and RESLVCNF.NET.SYS, as opposed to /etc/hosts and
/etc/resolv.conf on HP-UX.
Author
UCB (University of California at Berkeley)
Files
HOSTS.NET.SYS, RESLVCNF.NET.SYS
See Also
resolver, hosts