Standard C Library (libc, -lc)

The getprotoent, getprotobyname, and getprotobynumber functions each return a pointer to an object with the following structure containing the broken-out fields of a line in the network protocol data base, /etc/protocols.

struct	protoent {
	char	*p_name;	/* official name of protocol */
	char	**p_aliases;	/* alias list */
	int	p_proto;	/* protocol number */
};

The members of this structure are:

• p_name The official name of the protocol.
• p_aliases A zero terminated list of alternate names for the protocol.
• p_proto The protocol number.

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

The setprotoent 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 getprotobyname or getprotobynumber.

The endprotoent function closes the file.

The getprotobyname function and getprotobynumber sequentially search from the beginning of the file until a matching protocol name or protocol number is found, or until EOF is encountered.

Null pointer (0) returned on EOF or error.

• /etc/protocols

protocols(5)

The getprotoent, getprotobynumber, getprotobyname, setprotoent, and endprotoent functions appeared in

These functions use a thread-specific data space; if the data is needed for future use, it should be copied before any subsequent calls overwrite it. Only the Internet protocols are currently understood.