man3/getipnodebyname.3

.\" Copyright 2000 Sam Varshavchik <mrsam@courier-mta.com>
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.\" References: RFC 2553
.TH GETIPNODEBYNAME 3 2021-03-22 "Linux" "Linux Programmer's Manual"
.SH NAME
getipnodebyname, getipnodebyaddr, freehostent \- get network
hostnames and addresses
.SH SYNOPSIS
.nf
.B #include <sys/types.h>
.B #include <sys/socket.h>
.B #include <netdb.h>
.PP
.BI "struct hostent *getipnodebyname(const char *" name ", int " af ,
.BI "                                int " flags ", int *" error_num );
.BI "struct hostent *getipnodebyaddr(const void *" addr ", size_t " len ,
.BI "                                int " af ", int *" "error_num" );
.BI "void freehostent(struct hostent *" "ip" );
.fi
.SH DESCRIPTION
These functions are deprecated (and unavailable in glibc).
Use
.BR getaddrinfo (3)
and
.BR getnameinfo (3)
instead.
.PP
The
.BR getipnodebyname ()
and
.BR getipnodebyaddr ()
functions return the names and addresses of a network host.
These functions return a pointer to the
following structure:
.PP
.in +4n
.EX
struct hostent {
    char  *h_name;
    char **h_aliases;
    int    h_addrtype;
    int    h_length;
    char **h_addr_list;
};
.EE
.in
.PP
These functions replace the
.BR gethostbyname (3)
and
.BR gethostbyaddr (3)
functions, which could access only the IPv4 network address family.
The
.BR getipnodebyname ()
and
.BR getipnodebyaddr ()
functions can access multiple network address families.
.PP
Unlike the
.B gethostby
functions,
these functions return pointers to dynamically allocated memory.
The
.BR freehostent ()
function is used to release the dynamically allocated memory
after the caller no longer needs the
.I hostent
structure.
.SS getipnodebyname() arguments
The
.BR getipnodebyname ()
function
looks up network addresses for the host
specified by the
.I name
argument.
The
.I af
argument specifies one of the following values:
.TP
.B AF_INET
The
.I name
argument points to a dotted-quad IPv4 address or a name
of an IPv4 network host.
.TP
.B AF_INET6
The
.I name
argument points to a hexadecimal IPv6 address or a name
of an IPv6 network host.
.PP
The
.I flags
argument specifies additional options.
More than one option can be specified by bitwise OR-ing
them together.
.I flags
should be set to 0
if no options are desired.
.TP
.B AI_V4MAPPED
This flag is used with
.B AF_INET6
to request a query for IPv4 addresses instead of
IPv6 addresses; the IPv4 addresses will
be mapped to IPv6 addresses.
.TP
.B AI_ALL
This flag is used with
.B AI_V4MAPPED
to request a query for both IPv4 and IPv6 addresses.
Any IPv4 address found will be mapped to an IPv6 address.
.TP
.B AI_ADDRCONFIG
This flag is used with
.B 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
.B AI_V4MAPPED
flag.
.TP
.B AI_DEFAULT
This flag is equivalent to
.BR "(AI_ADDRCONFIG | AI_V4MAPPED)" .
.SS getipnodebyaddr() arguments
The
.BR getipnodebyaddr ()
function
looks up the name of the host whose
network address is
specified by the
.I addr
argument.
The
.I af
argument specifies one of the following values:
.TP
.B AF_INET
The
.I addr
argument points to a
.I struct in_addr
and
.I len
must be set to
.IR "sizeof(struct in_addr)" .
.TP
.B AF_INET6
The
.I addr
argument points to a
.I struct in6_addr
and
.I len
must be set to
.IR "sizeof(struct in6_addr)" .
.SH RETURN VALUE
NULL is returned if an error occurred, and
.I error_num
will contain an error code from the following list:
.TP
.B HOST_NOT_FOUND
The hostname or network address was not found.
.TP
.B NO_ADDRESS
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.
.TP
.B NO_RECOVERY
The domain name server returned a permanent failure response.
.TP
.B TRY_AGAIN
The domain name server returned a temporary failure response.
You might have better luck next time.
.PP
A successful query returns a pointer to a
.I hostent
structure that contains the following fields:
.TP
.I h_name
This is the official name of this network host.
.TP
.I h_aliases
This is an array of pointers to unofficial aliases for the same host.
The array is terminated by a null pointer.
.TP
.I h_addrtype
This is a copy of the
.I af
argument to
.BR getipnodebyname ()
or
.BR getipnodebyaddr ().
.I h_addrtype
will always be
.B AF_INET
if the
.I af
argument was
.BR AF_INET .
.I h_addrtype
will always be
.B AF_INET6
if the
.I af
argument was
.BR AF_INET6 .
.TP
.I h_length
This field will be set to
.I sizeof(struct in_addr)
if
.I h_addrtype
is
.BR AF_INET ,
and to
.I sizeof(struct in6_addr)
if
.I h_addrtype
is
.BR AF_INET6 .
.TP
.I 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.
.SH CONFORMING TO
RFC\ 2553.
.\" Not in POSIX.1-2001.
.SH NOTES
These functions were present in glibc 2.1.91-95, but were
removed again.
Several UNIX-like systems support them, but all
call them deprecated.
.SH SEE ALSO
.BR getaddrinfo (3),
.BR getnameinfo (3),
.BR inet_ntop (3),
.BR inet_pton (3)