GETHOSTBYNAME(3N)

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;

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), 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	*h_name;	/* official name of host */
    	char	**h_aliases;	/* alias list */
    	int	h_addrtype;	/* host 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:

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.

When using the nameserver, gethostbyname 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 environment variable ``HOSTALAIASES'' 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 format.

Sethostent 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 or gethostbyaddr. Otherwise, queries are performed using UDP datagrams.

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. 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_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 later time may succeed.

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

    NO_DATA
        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.

FILES
/etc/hosts

SEE ALSO
resolver(3), hosts(5), hostname(7), 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.