gethostbyaddr_r()

Get a network host entry

Synopsis:

#include <sys/types.h>
#include <sys/socket.h>
#include <netinet/in.h>
#include <arpa/inet.h>
#include <netdb.h>

struct hostent* gethostbyaddr_r( const void* addr,
                                 size_t length,
                                 int type,
                                 struct hostent* result,
                                 char* buffer,
                                 int buflen,
                                 int* h_errnop );

Library:

libsocket

Description:

The gethostbyaddr_r() function is a thread-safe version of gethostbyaddr(). This function gets the network host entry for the host specified by addr. The addr argument is the network address of the specified network family, type. The buffer for addr is at least length bytes.

If you need to convert a text-based address into the format necessary for use as gethostbyaddr_r()'s addr, see inet_pton().

The host entry is returned in the struct hostent pointed to by result. During the operation, buffer (and char buffer of at least buflen bytes) is used to store host database entries; buffer should be large enough to hold all of the data associated with the host entry. A 2K buffer is usually more than enough; a 256-byte buffer is safe in most cases.

The int that's pointed to by h_errnop is set to an herrno value if an error occurs.

Returns:

A pointer to result, or NULL if an error occurs.

Errors:

If an error occurs, the int pointed to by h_errnop is set to:

ERANGE

The supplied buffer isn't large enough to store the result.

HOST_NOT_FOUND

Authoritative answer: Unknown host.

NO_ADDRESS

No address associated with name; look for an MX record.

NO_DATA

Valid name, but no data record of the requested type. The name is known to the name server, but has no IP address associated with it -- this isn't a temporary error. Another type of request to the name server using this domain name will result in an answer (e.g. a mail-forwarder may be registered for this domain).

NO_RECOVERY

Unknown server error. An unexpected server failure was encountered. This is a nonrecoverable network error.

TRY_AGAIN

Nonauthoritative answer: Host name lookup failure. This is usually a temporary error and means that the local server didn't receive a response from an authoritative server. A retry at some later time may succeed.

Files:

/etc/hosts

Local host database file.

/etc/resolv.conf

Resolver configuration file.

Classification:

Unix

See also:

gethostbyaddr(), gethostbyname(), gethostbyname_r(), inet_ntop(), inet_pton()

/etc/hosts, /etc/resolv.conf in the Utilities reference