NAME

gethostbyname, gethostbyaddr, gethostent, sethostent, endhostent − 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()

DESCRIPTION

Gethostbyname and gethostbyaddr each return a pointer to an object with the following structure.  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.

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. 

Sethostent allows a request for the use of a connected socket using TCP 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 or gethostbyaddr.

Endhostent closes 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. 

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_RECOVERYThis is a non-recoverable error. 

NO_ADDRESSThe requested name is valid but does not have an IP address; this is not a temporary error.  This means another type of request to the name server will result in an answer. 

FILES

/etc/hosts

SEE ALSO

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

CAVEAT

Gethostent 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. 

Gethostent reads the next line of /etc/hosts, opening the file if necessary.

Sethostent is redefined to open and rewind the file.  If the stayopen argument is non-zero, the hosts data base will not be closed after each call to gethostbyname or gethostbyaddr. Endhostent is redefined to close the file. 

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. 

4.2 Berkeley Distribution  —  Revision 1.2 of 19/10/88