Getting The Port Address For The Desired Service - HP Rp3440-4 - 9000 - 0 MB RAM Programmer's Manual

Using Internet Datagram Sockets
Preparing Address Variables
#include <netdb.h>
struct hostent *hp; /* point to host info for name server host */
...
servaddr.sin_family = AF_INET;
hp = gethostbyname (argv[1]);
servaddr.sin_addr.s_addr = ((struct in_addr *)(hp->h_addr))->s_addr;
The argv[1] parameter is the host name specified in the client program
command line. Refer to the gethostent(3N) man page for more
information on gethostbyname.
Getting the Port Address for the Desired
Service
When a client process needs to use a service that is offered by some
server process, it must send a message to the server's socket. The client
process must know the port address for that socket. If the service is not
in /etc/services, you must add it.
getservbyname obtains the port address of the specified service from
/etc/services. getservbyname and its parameters are described in
the following table.
Include files:
System call:
Function result: pointer to struct servent containing port address,
Example:
#include <netdb.h>
struct servent *sp; /* pointer to service info */
...
sp = getservbyname ("example", "udp");
servaddr.sin_port = sp->s_port;
90
#include <netdb.h>
struct servent *getservbyname(name, proto)
char *name, *proto;
Parameter Description of Contents
name pointer to a valid service
name
proto pointer to the protocol to be
used
NULL pointer (0) if failure occurs.
INPUT Value
service name
udp or 0 if UDP is the
only protocol for the
service
Chapter 4