libbind_getnetent man page

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


#include <netdb.h>

struct netent *

struct netent *
getnetbyname(char name);

struct netent *
getnetbyaddr(unsigned long net, int type);

setnetent(int stayopen);



The getnetent(), getnetbyname(), and getnetbyaddr() subroutines each return a pointer to an object with the following structure containing the broken-out fields of a line in the networks database.

struct	netent { 
	char	*n_name;	/* official name of net */ 
	char	**n_aliases;	/* alias list */ 
	int	n_addrtype;	/* net number type */ 
	long	n_net;		/* net number */ 

The members of this structure are:

The official name of the network.
A zero-terminated list of alternate names for the network.
The type of the network number returned: AF_INET.
The network number. Network numbers are returned in machine byte order.

If the stayopen flag on a setnetent() subroutine is NULL, the networks database is opened. Otherwise, the setnetent() has the effect of rewinding the networks database. The endnetent() subroutine may be called to close the networks database when processing is complete.

The getnetent() subroutine simply reads the next line while getnetbyname() and getnetbyaddr() search until a matching name or net number is found (or until EOF is encountered). The type must be AF_INET. The getnetent() subroutine keeps a pointer in the database, allowing successive calls to be used to search the entire file.

Before a while loop using getnetent(), a call to setnetent() must be made in order to perform initialization; a call to endnetent() must be used after the loop. Both getnetbyname() and getnetbyaddr() make calls to setnetent() and endnetent().




Null pointer (0) returned on EOF or error.

See Also

networks(5), RFC 1101.


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


The data space used by these functions is static; 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.


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