NAME

gethostbyname, gethostbyaddr, gethostent, sethostent, endhostent, herror − get network host entry

SYNOPSIS

#include <netdb.h>

extern int h_errno;

struct hostent ∗gethostbyname(name)
char ∗name;

struct hostent ∗gethostbyaddr(addr, len, type)
char ∗addr; int len, type;

struct hostent ∗gethostent()

sethostent(stayopen)
int stayopen;

endhostent()

herror(string)
char ∗string;

extern int _host_verify;

DESCRIPTION

Gethostbyname and gethostbyaddr 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)), Network Information Service ( ypserv(8)), or broken-out fields from a line in /etc/hosts. Which function these routines use for a lookup depends on the contents of /etc/resolv.conf( resolver(5)).

structhostent {
char∗h_name;/∗ official name of host ∗/
char∗∗h_aliases;/∗ alias list ∗/
inth_addrtype;/∗ host address type ∗/
inth_length;/∗ length of address ∗/
char∗∗h_addr_list;/∗ list of addresses from name server ∗/
};
#defineh_addr  h_addr_list[0]/∗ address, for backward compatibility ∗/

The members of this structure are:

h_name Official name of the host. 

h_aliases A zero 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 zero terminated array of network addresses for the host.  Host addresses are returned in network byte order. 

h_addr The first address in h_addr_list; this is for backward compatiblity. 

If the name contains no dot, and if the environment variable “HOSTALAIASES” contains the name of an alias file, gethostbyname will search first the alias file for an alias matching the input name.  The named host in the current domain and its parents will be searched unless the name ends in a dot.  See hostname(7) for the domain search procedure and the alias file format.

If gethostbyaddr is used for authentication, external variable _host_verify should be make non-zero, and all answers obtained from name server will be verified using gethostbyname.

Gethostent extracts the information obtained from NIS or /etc/hosts file; one host per each call.  If bind function is used as resolver in /etc/resolv.conf file (see resolver(5)), gethostent always returns NULL.  When both of local and nis are specified, all informations from NIS and /etc/hosts are merged. 

Sethostent can be used to make gethostent begin its search from the beginning of the database.  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 or gethostbyaddr. Otherwise, queries are performed using UDP datagrams.

Endhostent closes the data file or the TCP connection. 

DIAGNOSTICS

Error return status from gethostbyname and gethostbyaddr is indicated by return of a null pointer.  The external integer h_errno 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-NULL, it is printed, followed by a colon and a space.  The error message is printed with a trailing newline. 

h_errno can have the following values:

HOST_NOT_FOUNDNo such host is known. 

TRY_AGAINThis is usually a temporary error and means that the local server did not receive a response from an authoritative server.  A retry at some later time may succeed. 

NO_RECOVERYSome unexpected server failure was encountered.  This is a non-recoverable error. 

NO_DATAThe 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. 

FILES

/etc/hosts, /etc/resolv.conf

SEE ALSO

resolver(3), hosts(5), resolver(5), hostname(7), named(8)

BUGS

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. 

NEWS-OSRelease 4.2.1R