GETNETENT(3)

NAME
getnetent, getnetent_r, getnetbyaddr, getnetbyaddr_r, getnetbyname, getnetbyname_r, setnetent, endnetent - get network entry

LIBRARY
libc

SYNOPSIS
#include <netdb.h>
struct netent *
getnetent(void);
int
getnetent_r(struct netent *ne, char *buffer, size_t buflen, struct netent **result, int *h_errnop);
struct netent *
getnetbyname(const char *name);
int
getnetbyname_r(const char *name, struct netent *ne, char *buffer, size_t buflen, struct netent **result, int *h_errnop);
struct netent *
getnetbyaddr(uint32_t net, int type);
int
getnetbyaddr_r(uint32_t addr, int af, struct netent *ne, char *buffer, size_t buflen, struct netent **result, int *h_errnop);
void
setnetent(int stayopen);
void
endnetent(void);

DESCRIPTION
The getnetent(), getnetbyname(), and 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, named(8), broken-out fields of a line in the network data base /etc/networks, or entries supplied by the yp(8) system. The order of the lookups is controlled by the `networks' entry in nsswitch.conf(5).

    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 */
    };

The members of this structure are:

n_name
    The official name of the network.

n_aliases
    A zero terminated list of alternate names for the network.

n_addrtype
    The type of the network number returned; currently only AF_INET.

n_net
    The network number. Network numbers are returned in machine byte order.

The getnetent() function reads the next line of the file, opening the file if necessary.

The setnetent() function opens and rewinds the file. If the stayopen flag is non-zero, the net data base will not be closed after each call to getnetbyname() or getnetbyaddr().

The endnetent() function closes the file.

The getnetbyname() function and getnetbyaddr() sequentially search from the beginning of the file until a matching net name or net address and type is found, or until EOF is encountered. The type argument must be AF_INET. Network numbers are supplied in host order.

The getnetent_r(), getnetbyaddr_r(), and getnetbyname_r() functions are reentrant versions of the above functions that take a pointer to a 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 netent structure which is used to store the results of the database lookup.

RETURN VALUES
The getnetent(), getnetbyaddr(), and getnetbyname() functions return a pointer to a netent structure on success or a null pointer if end-of-file is reached or an error occurs.

The getnetent_r(), getnetbyaddr_r(), and getnetbyname_r() functions return 0 on success or -1 if end-of-file is reached or an error occurs.

FILES
/etc/networks
/etc/nsswitch.conf
/etc/resolv.conf

SEE ALSO
networks(5)

STANDARDS
The getnetent(), getnetbyaddr(), getnetbyname(), setnetent(), and endnetent() functions conform to p1003.1-2004.

The getnetent_r(), getnetbyaddr_r(), and getnetbyname_r() functions are not currently standardized.

HISTORY
The getnetent(), getnetbyaddr(), getnetbyname(), setnetent(), and endnetent() functions appeared in 4.2BSD.

The getnetent_r(), getnetbyaddr_r(), and getnetbyname_r() functions appeared in DragonFly 2.1.

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.