#include <netdb.h> struct servent *getservent(void); struct servent *getservbyname(const char *name, const char *proto); struct servent *getservbyport(int port, const char *proto); void setservent(int stayopen); void endservent(void);
The getservbyname() function returns a servent structure for the entry from the database that matches the service name using protocol proto. If proto is NULL, any protocol will be matched. A connection is opened to the database if necessary.
The getservbyport() function returns a servent structure for the entry from the database that matches the port port (given in network byte order) using protocol proto. If proto is NULL, any protocol will be matched. A connection is opened to the database if necessary.
The setservent() function opens a connection to the database, and sets the next entry to the first entry. If stayopen is non-zero, then the connection to the database will not be closed between calls to one of the getserv*() functions.
The endservent() function closes the connection to the database.
The servent structure is defined in <netdb.h> as follows:
struct servent {
    char  *s_name;       /* official service name */
    char **s_aliases;    /* alias list */
    int    s_port;       /* port number */
    char  *s_proto;      /* protocol to use */
}
The members of the servent structure are: