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GETSERVENT(3) Library Functions Manual GETSERVENT(3)

getservent, getservent_r, getservbyport, getservbyport_r, getservbyname, getservbyname_r, setservent, setservent_r, endservent, endservent_r —
get service entry

#include <netdb.h>

struct servent *
getservent(void);

int
getservent_r(struct servent *servent, struct servent_data *servent_data);

struct servent *
getservbyname(const char *name, const char *proto);

int
getservbyname_r(const char *name, const char *proto, struct servent *servent, struct servent_data *servent_data);

struct servent *
getservbyport(int port, const char *proto);

int
getservbyport_r(int port, const char *proto, struct servent *servent, struct servent_data *servent_data);

void
setservent(int stayopen);

void
setservent_r(int stayopen, struct servent_data *servent_data);

void
endservent(void);

void
endservent_r(struct servent_data *servent_data);

The getservent(), getservbyname(), and getservbyport() functions each return a pointer to an object with the following structure containing the broken-out fields of a line in the network services database, /etc/services. 
struct	servent {
	char	*s_name;	/* official name of service */
	char	**s_aliases;	/* alias list */
	int	s_port;		/* port service resides at */
	char	*s_proto;	/* protocol to use */
};

The members of this structure are:

s_name
The official name of the service.
s_aliases
A null-terminated list of alternate names for the service.
s_port
The port number at which the service resides. Port numbers are returned in network byte order.
s_proto
The name of the protocol to use when contacting the service.

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

The setservent() function opens and rewinds the file. If the stayopen flag is non-zero, the services database will not be closed after each call to getservbyname() or getservbyport().

The endservent() function closes the file.

The getservbyname() and getservbyport() functions sequentially search from the beginning of the file until a matching protocol name or port number (specified in network byte order) is found, or until EOF is encountered. If a protocol name is also supplied (non-null), searches must also match the protocol.

The getservent_r(), getservbyport_r(), getservbyname_r(), setservent_r(), and endservent_r() functions are reentrant versions of the above functions that take a pointer to a servent_data 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.

The getservent_r(), getservbyport_r(), and getservbyname_r() functions also take a pointer to a servent structure which is used to store the results of the database lookup.

The getservent(), getservbyport(), and getservbyname() functions return a pointer to a servent structure on success or a null pointer if end-of-file is reached or an error occurs.

The getservent_r(), getservbyport_r(), and getservbyname_r() functions return 0 on success or -1 if end-of-file is reached or an error occurs.

/etc/services
 

getprotoent(3), services(5)

The getservent(), getservbynumber(), getservbyname(), setservent(), and endservent() functions conform to IEEE Std 1003.1-2004 (“POSIX.1”).

The getservent_r(), getservbyport_r(), getservbyname_r(), setservent_r(), and endservent_r() functions are not currently standardized. This implementation follows the API used by HP, IBM, and Digital.

The getservent(), getservbyport(), getservbyname(), setservent(), and endservent() functions appeared in 4.2BSD.

The getservent_r(), getservbyport_r(), getservbyname_r(), setservent_r(), and endservent_r() functions appeared in OpenBSD 3.7.

The non-reentrant functions use static data storage; if the data is needed for future use, it should be copied before any subsequent calls overwrite it. Expecting port numbers to fit in a 32-bit quantity is probably naive.
June 5, 2013 OpenBSD-current