Service Names – servent

An Internet family service resides at a specific, well-known port, and uses a particular protocol. A service-name-to-port-number mapping is described by the servent structure that is defined in getprotoent(3SOCKET):

struct servent {
    char    *s_name;        /* official service name */
    char    **s_aliases;    /* alias list */
    int     s_port;         /* port number, network byte order */
    char    *s_proto;       /* protocol to use */
};

getservbyname(3SOCKET) maps service names and, optionally, a qualifying protocol to a servent structure. The call:

sp = getservbyname("telnet", (char *) 0);

returns the service specification of a telnet server that is using any protocol. The call:

sp = getservbyname("telnet", "tcp");

returns the telnet server that uses the TCP protocol. getservbyport(3SOCKET) and getservent(3SOCKET) are also provided. getservbyport(3SOCKET) has an interface that is similar to the interface used by getservbyname(3SOCKET). You can specify an optional protocol name to qualify lookups.