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.\"     @(#)getnetent.3	8.1 (Berkeley) 6/4/93
.\" $FreeBSD: src/lib/libc/net/getnetent.3,v 1.23 2007/01/09 00:28:02 imp Exp $
.\"
.Dd May 6, 2019
.Dt GETNETENT 3
.Os
.Sh NAME
.Nm getnetent ,
.Nm getnetent_r ,
.Nm getnetbyaddr ,
.Nm getnetbyaddr_r ,
.Nm getnetbyname ,
.Nm getnetbyname_r ,
.Nm setnetent ,
.Nm endnetent
.Nd get network entry
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In netdb.h
.Ft struct netent *
.Fn getnetent void
.Ft int
.Fn getnetent_r "struct netent *ne" "char *buffer" "size_t buflen" "struct netent **result" "int *h_errnop"
.Ft struct netent *
.Fn getnetbyname "const char *name"
.Ft int
.Fn getnetbyname_r "const char *name" "struct netent *ne" "char *buffer" "size_t buflen" "struct netent **result" "int *h_errnop"
.Ft struct netent *
.Fn getnetbyaddr "uint32_t net" "int type"
.Ft int
.Fn getnetbyaddr_r "uint32_t addr" "int af" "struct netent *ne" "char *buffer" "size_t buflen" "struct netent **result" "int *h_errnop"
.Ft void
.Fn setnetent "int stayopen"
.Ft void
.Fn endnetent void
.Sh DESCRIPTION
The
.Fn getnetent ,
.Fn getnetbyname ,
and
.Fn getnetbyaddr
functions
each return a pointer to an object with the
following structure describing an internet network.
This structure contains either the information obtained
from the nameserver,
.Xr named 8 ,
broken-out fields of a line in the network data base
.Pa /etc/networks ,
or entries supplied by the
.Xr yp 8
system.
The order of the lookups is controlled by the
`networks' entry in
.Xr nsswitch.conf 5 .
.Bd -literal -offset indent
struct	netent {
	char		*n_name;	/* official name of net */
	char		**n_aliases;	/* alias list */
	int		n_addrtype;	/* net number type */
	uint32_t	n_net;		/* net number */
};
.Ed
.Pp
The members of this structure are:
.Bl -tag -width n_addrtype
.It Fa n_name
The official name of the network.
.It Fa n_aliases
A zero terminated list of alternate names for the network.
.It Fa n_addrtype
The type of the network number returned; currently only
.Dv AF_INET .
.It Fa n_net
The network number.
Network numbers are returned in machine byte
order.
.El
.Pp
The
.Fn getnetent
function
reads the next line of the file, opening the file if necessary.
.Pp
The
.Fn setnetent
function
opens and rewinds the file.
If the
.Fa stayopen
flag is non-zero,
the net data base will not be closed after each call to
.Fn getnetbyname
or
.Fn getnetbyaddr .
.Pp
The
.Fn endnetent
function
closes the file.
.Pp
The
.Fn getnetbyname
function
and
.Fn getnetbyaddr
sequentially search from the beginning
of the file until a matching
net name or
net address and type is found,
or until
.Dv EOF
is encountered.
The
.Fa type
argument
must be
.Dv AF_INET .
Network numbers are supplied in host order.
.Pp
The
.Fn getnetent_r ,
.Fn getnetbyaddr_r ,
and
.Fn getnetbyname_r
functions are reentrant versions of the above functions that take a
pointer to a
.Vt netent
structure which is used to store state information.
The structure must be zero-filled before it is used
and should be considered opaque for the sake of portability.
These functions also take a pointer to another
.Vt netent
structure which is used to store the results of the database lookup.
.Sh RETURN VALUES
The
.Fn getnetent ,
.Fn getnetbyaddr ,
and
.Fn getnetbyname
functions return a pointer to a
.Vt netent
structure on success or a null pointer if end-of-file
is reached or an error occurs.
.Pp
The
.Fn getnetent_r ,
.Fn getnetbyaddr_r ,
and
.Fn getnetbyname_r
functions return 0 on success or \-1 if end-of-file
is reached or an error occurs.
.Sh FILES
.Bl -tag -width ".Pa /etc/nsswitch.conf" -compact
.It Pa /etc/networks
.It Pa /etc/nsswitch.conf
.It Pa /etc/resolv.conf
.El
.Sh SEE ALSO
.Xr networks 5
.Pp
.%T RFC 1101
.Sh STANDARDS
The
.Fn getnetent ,
.Fn getnetbyaddr ,
.Fn getnetbyname ,
.Fn setnetent ,
and
.Fn endnetent
functions conform to
.St -p1003.1-2004 .
.Pp
The
.Fn getnetent_r ,
.Fn getnetbyaddr_r ,
and
.Fn getnetbyname_r
functions are not currently standardized.
.Sh HISTORY
The
.Fn getnetent ,
.Fn getnetbyaddr ,
.Fn getnetbyname ,
.Fn setnetent ,
and
.Fn endnetent
functions appeared in
.Bx 4.2 .
.Pp
The
.Fn getnetent_r ,
.Fn getnetbyaddr_r ,
and
.Fn getnetbyname_r
functions appeared in
.Dx 2.1 .
.Sh BUGS
The data space used by
these functions is thread-specific; if future use requires the data, it should be
copied before any subsequent calls to these functions overwrite it.
Only Internet network
numbers are currently understood.
Expecting network numbers to fit
in no more than 32 bits is probably
naive.