Get a network host entry, in a thread-safe manner
struct hostent * gethostbyaddr_r(
const void * addr,
struct hostent * result,
char * buffer,
int * h_errnop );
- A pointer to the binary-format (i.e., not NULL-terminated)
address in network byte order.
- The length, in bytes, of addr.
- The type of address. Currently, this must be AF_INET.
- A pointer to a struct hostent where the function can
store the host entry.
- A pointer to a buffer that the function can use during the operation
to store host database entries; buffer should be large enough to
hold all of the data associated with the host entry.
A 2 KB buffer is usually more than enough; a 256-byte buffer is safe in most
- The length of the area pointed to by buffer.
- A pointer to a location where the function can store an
value if an error occurs.
Use the -l socket option to
to link against this library.
The gethostbyaddr_r() function is a thread-safe version of
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
A pointer to result, or NULL if an error occurs.
If an error occurs, the int pointed to by h_errnop
is set to:
- The supplied buffer isn't large enough to store the result.
- Authoritative answer: Unknown host.
- No address associated with name; look for an MX record.
- 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).
- Unknown server error. An unexpected server failure was encountered.
This is a nonrecoverable network error.
- 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.
- Local host database file.
- Name-service switch configuration file.
in the Utilities Reference