Mapping service names (Internet domain)

Service names are a bit more complex. A service is expected to reside at a specific ``port'' and employ a particular communication protocol. This view is consistent with the Internet domain, but inconsistent with other network architectures. Further, a service may reside on multiple ports or support multiple protocols. If either of these occurs, the higher level library routines will have to be bypassed in favor of homegrown routines similar to the gethostbynameandnet routine.

A service mapping is described by the servent structure:

struct  servent {
        char        *s_name;
        char       **s_aliases;
        int          s_port;
        char        *s_proto;
        }

*s_name

is the official service name

**s_aliases

is the alias list.

s_port

is the port number.

*s_proto

is the protocol to use

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

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

The routines getservbyport(SLIB) and getservent(SLIB) are also provided. The getservbyport routine has an interface similar to that provided by getservbyname. An optional protocol name may be specified to qualify lookups.