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GETNETENT(3) Library Functions Manual GETNETENT(3)

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

Standard C Library (libc, -lc)

#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);

int
getnetent_r(struct netent *ne, char *buffer, size_t buflen, struct netent **result, int *h_errnop);

int
getnetbyaddr_r(uint32_t net, int type, struct netent *ne, char *buffer, size_t buflen, struct netent **result, int, *h_errorp");

int
getnetbyname_r(const char *name, struct netent *ne, char *buffer, size_t buflen, struct netent **result, int *h_errorp);

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, 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.

Functions with the suffix provide reentrant versions of their respective counterparts. The caller must supply five additional parameters: a struct netent variable to be filled on success, a buffer of buflen bytes in size, a struct netent result variable that will point to the result on success or be set to NULL on failure or if the name is not found. The h_errnop variable will be filled with the error code if any. All these functions return 0 on success.

/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 27, 2022 dev