man3/getnetent.3

.\" Copyright 1993 David Metcalfe (david@prism.demon.co.uk)
.\"
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.\" References consulted:
.\"     Linux libc source code
.\"     Lewine's _POSIX Programmer's Guide_ (O'Reilly & Associates, 1991)
.\"     386BSD man pages
.\" Modified Sat Jul 24 21:48:06 1993 by Rik Faith (faith@cs.unc.edu)
.TH GETNETENT 3  2020-12-21 "GNU" "Linux Programmer's Manual"
.SH NAME
getnetent, getnetbyname, getnetbyaddr, setnetent, endnetent \-
get network entry
.SH SYNOPSIS
.nf
.B #include <netdb.h>
.PP
.B struct netent *getnetent(void);
.PP
.BI "struct netent *getnetbyname(const char *" name );
.BI "struct netent *getnetbyaddr(uint32_t " net ", int " type );
.PP
.BI "void setnetent(int " stayopen );
.B void endnetent(void);
.fi
.SH DESCRIPTION
The
.BR getnetent ()
function reads the next entry from the networks database
and returns a
.I netent
structure containing
the broken-out fields from the entry.
A connection is opened to the database if necessary.
.PP
The
.BR getnetbyname ()
function returns a
.I netent
structure
for the entry from the database
that matches the network
.IR name .
.PP
The
.BR getnetbyaddr ()
function returns a
.I netent
structure
for the entry from the database
that matches the network number
.I net
of type
.IR type .
The
.I net
argument must be in host byte order.
.PP
The
.BR setnetent ()
function opens a connection to the database,
and sets the next entry to the first entry.
If
.I stayopen
is nonzero,
then the connection to the database
will not be closed between calls to one of the
.BR getnet* ()
functions.
.PP
The
.BR endnetent ()
function closes the connection to the database.
.PP
The
.I netent
structure is defined in
.I <netdb.h>
as follows:
.PP
.in +4n
.EX
struct netent {
    char      *n_name;     /* official network name */
    char     **n_aliases;  /* alias list */
    int        n_addrtype; /* net address type */
    uint32_t   n_net;      /* network number */
}
.EE
.in
.PP
The members of the
.I netent
structure are:
.TP
.I n_name
The official name of the network.
.TP
.I n_aliases
A NULL-terminated list of alternative names for the network.
.TP
.I n_addrtype
The type of the network number; always
.BR AF_INET .
.TP
.I n_net
The network number in host byte order.
.SH RETURN VALUE
The
.BR getnetent (),
.BR getnetbyname (),
and
.BR getnetbyaddr ()
functions return a pointer to a
statically allocated
.I netent
structure, or a null pointer if an
error occurs or the end of the file is reached.
.SH FILES
.TP
.I /etc/networks
networks database file
.SH ATTRIBUTES
For an explanation of the terms used in this section, see
.BR attributes (7).
.ad l
.nh
.TS
allbox;
lb lb lbx
l l l.
Interface	Attribute	Value
T{
.BR getnetent ()
T}	Thread safety	T{
MT-Unsafe race:netent
race:netentbuf env locale
T}
T{
.BR getnetbyname ()
T}	Thread safety	T{
MT-Unsafe race:netbyname
env locale
T}
T{
.BR getnetbyaddr ()
T}	Thread safety	T{
MT-Unsafe race:netbyaddr
locale
T}
T{
.BR setnetent (),
.BR endnetent ()
T}	Thread safety	T{
MT-Unsafe race:netent env
locale
T}
.TE
.hy
.ad
.sp 1
In the above table,
.I netent
in
.I race:netent
signifies that if any of the functions
.BR setnetent (),
.BR getnetent (),
or
.BR endnetent ()
are used in parallel in different threads of a program,
then data races could occur.
.SH CONFORMING TO
POSIX.1-2001, POSIX.1-2008, 4.3BSD.
.SH NOTES
In glibc versions before 2.2, the
.I net
argument of
.BR getnetbyaddr ()
was of type
.IR long .
.SH SEE ALSO
.BR getnetent_r (3),
.BR getprotoent (3),
.BR getservent (3)
.\" .BR networks (5)
.br
RFC\ 1101