Technical Reference: Communications, Volume 2

gethostbyaddr_r Subroutine

Purpose

Gets network host entry by address.

Library

Standard C Library (libc.a)
(libbind)
(libnis)
(liblocal)

Syntax

#include <netdb.h>
int gethostbyadd_r(Addr, Len, Type, Htent, Ht_data)
const char *Addr, size_t Len, int Type, struct hostent *Htent, struct hostent_data *Ht_data;

Description

This function internally calls the gethostbyaddr subroutine and stores the value returned by the gethostbyaddr subroutine to the hostent structure.

Parameters

Addr	Points to the host address which is a constant string.
Len	Specifies the length of the address.
Type	Specifies the domain type of the host address. This works only on the address family AF_INET.
Htent	Points to a hostent structure which is used to store the return value of the gethostaddr subroutine.
Ht_data	Points to a hostent_data structure.

Return Values

The function returns a 0 if successful and a -1 if unsuccessful.

Note

The return value of the gethostbyaddr subroutine points to static data that is overwritten by subsequent calls. This data must be copied at every call to be saved for use by subsequent calls. The gethostbyaddr_r subroutine solves this problem.

If the Name parameter is a hostname, this subroutine searches for a machine with that name as an IP address. Because of this, use the gethostbyname_r subroutine.

Error Codes

The gethostbyaddr_r subroutine is unsuccessful if any of the following errors occur:

HOST_NOT_FOUND	The host specified by the Name parameter was not found.
TRY_AGAIN	The local server did not receive a response from an authoritative server. Try again later.
NO_RECOVERY	Indicates an unrecoverable error occured.
NO_ADDRESS	The requested Name parameter is valid but does not have an Internet address at the name server.
SERVICE_UNAVAILABLE	None of the name services specified are running or available.
EINVAL	The hostent pointer is NULL

Files

/etc/hosts	Contains the host name data base.
/etc/resolv.conf	Contains the name server and domain name.
/etc/netsvc.conf	Contains the name services ordering.
/usr/include/netdb.h	Contains the network database structure.

Related Information

endhostent_r Subroutine, gethostbyaddr_r Subroutine, gethostent_r Subroutine, and sethostent_r Subroutine.