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GETNETENT(3) Library Functions Manual GETNETENT(3)

getnetent, getnetbyaddr, getnetbyname, setnetent, endnetent — get network entry

library “libc”

#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);

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

The () 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 () function closes the file.

The () function and () 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.

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

Null pointer returned on EOF or error.

networks(5)

RFC 1101

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

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.

June 4, 1993 FreeBSD-12.0