gethostbyaddr()

The gethostbyaddr() call tries to resolve the IP address to a host name. The resolution attempted depends on how the resolver is configured and if any local host tables exist. If the symbol RESOLVE_VIA_LOOKUP is defined before including MANIFEST.H, gethostbyaddr() only uses local host tables and name servers are not used. See z/OS Communications Server: IP Configuration Guide for information about configuring the resolver and using local host tables.

#include <manifest.h>
#include <netdb.h>
struct hostent *gethostbyaddr(char *addr, int addrlen, int domain)

Parameter: Description
addr: Points to an unsigned long value containing the address of the host
addrlen: Size of addr in bytes
domain: Address domain supported (AF_INET)

The gethostbyaddr() call points to hostent structure for the host address specified on the call.

The NETDB.H header file defines the hostent structure, and contains the following elements:

Element: Description
h_name: The address of the official name of the host
h_aliases: A pointer to a zero-terminated list of addresses pointing to alternate names for the host
h_addrtype: The type of host address returned; currently, always set to AF_INET
h_length: The length of the host address, in bytes
h_addr: A pointer to a zero-terminated list of addresses pointing to the internet host addresses returned by the call

Return values

The return value points to static data that is overwritten by subsequent calls. A pointer to a hostent structure indicates success. A NULL pointer indicates an error or end-of-file. When a NULL pointer or 0 is returned, the value of errno is indeterminate: the output from a tcperror() call cannot be validated. The global variable h_errno identifies the specific error.

h_errno: Description
HOST_NOT_FOUND: The name specified is unknown, the address domain specified is not supported, or the address length specified is not valid.
TRY_AGAIN: Temporary error; information not currently accessible.
NO_RECOVERY: Fatal error occurred.

Related calls

gethostent(), sethostent(), endhostent()