gethostbyaddr(3) Library Functions Manual gethostbyaddr(3)
NAME
gethostbyaddr, gethostbyaddr_r - Gets a network host entry by address
LIBRARY
Standard C Library (libc.so, libc.a)
SYNOPSIS
#include <netdb.h>
struct hostent *gethostbyaddr( const void *addr, size_t len, int type) ;
[Tru64 UNIX] The following obsolete routine is supported in order to maintain backward compatibility with previous versions of the operat-
ing system. You should not use it in new designs. int *gethostbyaddr_r( const char *addr, int len, int type, struct
hostent *hptr, struct hostent_data *hdptr);
[Tru64 UNIX] The following definition of the gethostbyaddr() routine does not conform to current standards and is supported only for
backward compatibility (see standards(5)): struct hostent *gethostbyaddr( const char *addr, int len, int type) ;
STANDARDS
Interfaces documented on this reference page conform to industry standards as follows:
gethostbyaddr(): XNS4.0
Refer to the standards(5) reference page for more information about industry standards and associated tags.
PARAMETERS
Specifies an Internet address in network order. Specifies the number of bytes in an Internet address. Specifies the Internet domain
address format (AF_INET). [Tru64 UNIX] Is data for the host database. The netdb.h header file defines the hostent_data structure.
[Tru64 UNIX] Points to the hostent structure. The netdb.h header file defines the hostent structure.
DESCRIPTION
The gethostbyaddr() routine returns a pointer to a structure of type hostent. Its members specify data obtained from either the local
/etc/hosts file or one of the files distributed by DNS/BIND or NIS. To determine which file or files to search, and in which order, the
system uses the switches in the /etc/svc.conf file. The netdb.h header file defines the hostent structure.
The gethostbyaddr() routine searches the network host database sequentially until a match with the addr and type parameters occurs. The
len parameter must specify the number of bytes in an Internet address. The addr parameter must specify the address in network order. The
type parameter must be the constant AF_INET, which specifies the Internet Protocol Version 4 (IPv4) address format. When EOF (End-of-File)
is reached without a match, an error value is returned.
If using DNS/BIND, the information is obtained from a name server specified in the /etc/resolv.conf file. When the name server is not run-
ning, the gethostbyaddr() routine searches the local hosts name file.
Use the endhostent() routine to close the /etc/hosts file.
NOTES
The gethostbyaddr() routine returns a pointer to thread-specific data. Subsequent calls to this or a related routine from the same thread
overwrite this data.
[Tru64 UNIX] The gethostbyaddr_r() routine is an obsolete reentrant version of the gethostbyaddr() routine. It is supported in order to
maintain backward compatibility with previous versions of the operating system and should not be used in new designs. Note that you must
zero-fill the hdptr structure before its first access by the gethostbyaddr_r() routine.
RETURN VALUES
Upon successful completion, the gethostbyaddr() routine returns a pointer to a hostent structure. If it reaches the end of the network
hostname database, it returns a null pointer.
[Tru64 UNIX] Upon successful completion, the gethostbyaddr_r() routine stores the hostent structure in hptr, and returns a value of 0
(zero). Upon failure, it returns a value of -1.
ERRORS
If the gethostbyaddr() or gethostbyaddr_r() routine call fails, h_errno is set to one of the following values: Host is unknown. The server
recognized the request and the name, but no address is available for the name. Another type of name server request may be successful. An
unexpected server failure occurred. This is a nonrecoverable error. A transient error occurred, for example, the server did not respond.
A retry at some later time may be successful.
[Tru64 UNIX] If any of the following conditions occurs, the gethostbyaddr_r() routine sets errno to the corresponding value: The name,
hptr, or hdptr is invalid, or type is not AF_INET.
FILES
This file is the Internet network hostname database. Each record in the file occupies a single line and has three fields consisting of the
host address, official hostname, and aliases. The resolver configuration file. The database service selection configuration file.
RELATED INFORMATION
routines: endhostent(3), gethostbyname(3), sethostent(3).
Files: hosts(4), resolv.conf(4), svc.conf(4).
Networks: bind_intro(7), nis_intro(7).
Standards: standards(5) delim off
gethostbyaddr(3)