ares_gethostbyaddr - Initiate a host query by address
typedef void (*ares_host_callback)(void *arg, int status,
int timeouts, struct hostent *hostent)
void ares_gethostbyaddr(ares_channel channel, const void *addr,
int addrlen, int family, ares_host_callback callback,
function initiates a host query by address on the
name service channel identified by channel
. The parameters addr
give the address as a series of bytes, and family
gives the type of address. When the query is complete or has failed, the ares
library will invoke callback
. Completion or failure of the query may
happen immediately, or may happen during a later call to
The callback argument arg
is copied from the ares_gethostbyaddr
. The callback argument status
indicates whether the
query succeeded and, if not, how it failed. It may have any of the following
- The host lookup completed successfully.
- The ares library does not know how to look up addresses of
- The address addr was not found.
- Memory was exhausted.
- The query was cancelled.
- The name service channel channel is being destroyed;
the query will not be completed.
The callback argument timeouts
reports how many times a query timed out
during the execution of the given request.
On successful completion of the query, the callback argument hostent
points to a struct hostent
containing the name of the host returned by
the query. The callback need not and should not attempt to free the memory
pointed to by hostent
; the ares library will free it when the callback
returns. If the query did not complete successfully, hostent
Greg Hudson, MIT Information Systems
Copyright 1998 by the Massachusetts Institute of Technology.