getnetent(3) Library Functions Manual getnetent(3)
NAME
getnetent, getnetbyname, getnetbyaddr, setnetent, endnetent - get net-
work entry
LIBRARY
Standard C library (libc, -lc)
SYNOPSIS
#include <netdb.h>
struct netent *getnetent(void);
struct netent *getnetbyname(const char *name);
struct netent *getnetbyaddr(uint32_t net, int type);
void setnetent(int stayopen);
void endnetent(void);
DESCRIPTION
The getnetent() function reads the next entry from the networks database
and returns a netent structure containing the broken-out fields from the
entry. A connection is opened to the database if necessary.
The getnetbyname() function returns a netent structure for the entry
from the database that matches the network name.
The getnetbyaddr() function returns a netent structure for the entry
from the database that matches the network number net of type type. The
net argument must be in host byte order.
The setnetent() function opens a connection to the database, and sets
the next entry to the first entry. If stayopen is nonzero, then the
connection to the database will not be closed between calls to one of
the getnet*() functions.
The endnetent() function closes the connection to the database.
The netent structure is defined in <netdb.h> as follows:
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 */
}
The members of the netent structure are:
n_name The official name of the network.
n_aliases
A NULL-terminated list of alternative names for the network.
n_addrtype
The type of the network number; always AF_INET.
n_net The network number in host byte order.
RETURN VALUE
The getnetent(), getnetbyname(), and getnetbyaddr() functions return a
pointer to a statically allocated netent structure, or a null pointer if
an error occurs or the end of the file is reached.
FILES
/etc/networks
networks database file
ATTRIBUTES
For an explanation of the terms used in this section, see attributes(7).
┌────────────────┬───────────────┬─────────────────────────────────────┐
│ Interface │ Attribute │ Value │
├────────────────┼───────────────┼─────────────────────────────────────┤
│ getnetent() │ Thread safety │ MT-Unsafe race:netent │
│ │ │ race:netentbuf env locale │
├────────────────┼───────────────┼─────────────────────────────────────┤
│ getnetbyname() │ Thread safety │ MT-Unsafe race:netbyname env locale │
├────────────────┼───────────────┼─────────────────────────────────────┤
│ getnetbyaddr() │ Thread safety │ MT-Unsafe race:netbyaddr locale │
├────────────────┼───────────────┼─────────────────────────────────────┤
│ setnetent(), │ Thread safety │ MT-Unsafe race:netent env locale │
│ endnetent() │ │ │
└────────────────┴───────────────┴─────────────────────────────────────┘
In the above table, netent in race:netent signifies that if any of the
functions setnetent(), getnetent(), or endnetent() are used in parallel
in different threads of a program, then data races could occur.
STANDARDS
POSIX.1-2008.
HISTORY
POSIX.1-2001, 4.3BSD.
Before glibc 2.2, the net argument of getnetbyaddr() was of type long.
SEE ALSO
getnetent_r(3), getprotoent(3), getservent(3)
RFC 1101
Linux man-pages 6.9.1 2024-05-02 getnetent(3)
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