getipnodebyname, getipnodebyaddr, freehostent - get net
work host names and addresses
SYNOPSIS
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
struct hostent *getipnodebyname(const char *name,
int af, int flags,
int *error_num);
struct hostent *getipnodebyaddr(const void *addr,
size_t len, int af,
int *error_num);
void freehostent(struct hostent *ip);
DESCRIPTION
The getipnodebyname(3) and getipnodebyaddr(3) functions
return the names and addresses of a network host. These
functions return a pointer to the following structure:
struct hostent {
char *h_name;
char **h_aliases;
int h_addrtype;
int h_length;
char **h_addr_list;
};
These functions replace the gethostbyname(3) and gethost
byaddr(3) functions, which could only access the IPv4 net
work address family. The getipnodebyname(3) and getipn
odebyaddr(3) functions can access multiple network address
families.
Unlike the gethostby functions, these functions return
pointers to dynamically allocated memory. The freehos
tent(3) function is used to release the dynamically allo
cated memory after the caller no longer needs the hostent
structure.
getipnodebyname parameters
The getipnodebyname(3) function looks up network addresses
for the host specified by the name parameter. The af
parameter specifies one of the following values:
AF_INET
The name parameter points to a dotted-quad IPv4
address or a name of an IPv4 network host.
The name parameter points to a hexadecimal IPv6
address or a name of an IPv6 network host.
The flags parameter specifies additional options. More
than one option can be specified by logically OR-ing them
together. flags should be set to 0 if no options are
desired.
AI_V4MAPPED
This flag is used with AF_INET6 to request a query
for IPv4 addresses instead of IPv6 addresses; the
IPv4 addresses will be mapped to IPv6 addresses.
AI_ALL This flag is used with AI_V4MAPPED to request a
query for both IPv4 and IPv6 addresses. Any IPv4
address found will be mapped to an IPv6 address.
AI_ADDRCONFIG
This flag is used with AF_INET6 to further request
that queries for IPv6 addresses should not be made
unless the system has at least one IPv6 address
assigned to a network interface, and that queries
for IPv4 addresses should not be made unless the
system has at least one IPv4 address assigned to a
network interface. This flag may be used by itself
or with the AI_V4MAPPED flag.
AI_ALL This flag is equivalent to (AI_ADDRCONFIG |
AI_V4MAPPED).
getipnodebyaddr parameters
The getipnodebyaddr(3) function looks up the name of the
host whose network address is specified by the addr param
eter. The af parameter specifies one of the following
values:
AF_INET
The addr parameter points to a struct in_addr and
len must be set to sizeof(struct in_addr).
AF_INET6
The addr parameter points to a struct in6_addr and
len must be set to sizeof(struct in6_addr).
RETURN VALUE
A null pointer is returned if an error occurred, and
error_num will contain an error code from the following
list:
HOST_NOT_FOUND
The host name or network address was not found.
The domain name server recognized the network
address or name, but no answer was returned. This
can happen if the network host has only IPv4
addresses and a request has been made for IPv6
information only, or vice versa.
NO_RECOVERY
The domain name server returned a permanent failure
response.
TRY_AGAIN
The domain name server returned a temporary failure
response. You might have better luck next time.
A successful query returns a pointer to a hostent struc
ture that contains the following fields:
h_name This is the official name of this network host.
h_aliases
This is an array of pointers to unofficial aliases
for the same host. The array is terminated by a
null pointer.
h_addrtype
This is a copy of the af parameter to getipnodeby
name(3) or getipnodebyaddr(3). h_addrtype will
always be AF_INET if the af parameter was AF_INET.
h_addrtype will always be AF_INET6 if the af param
eter was AF_INET6.
h_length
This field will be set to sizeof(struct in_addr) if
h_addrtype is AF_INET, and to sizeof(struct
in6_addr) if h_addrtype is AF_INET6.
h_addr_list
This is an array of one or more pointers to network
address structures for the network host. The array
is terminated by a null pointer.
SEE ALSO
getaddrinfo(3), inet_ntop(3), inet_pton(3)
Man(1) output converted with
man2html