Writing a Single-threaded C RPC Client Application

This document describes in six steps how to write your first C client program.

The example given here demonstrates how to write a single-threaded C RPC client application. It demonstrates an implicit broker logon (because no broker logon/logoff calls are implemented), where it is required to switch on the AUTOLOGON feature in the broker attribute file.

The following steps describe how to write a single-threaded C client program. We recommend reading them first before writing your first RPC client program and following them where appropriate.

Step 1: Base Declarations Required by the C Wrapper

Step 1a: Include the Generated Header File

Define the generated client header file. This header file includes the RPC runtime header file erx.h and defines structures and prototypes for your RPC requests. 

/* include generated header file */
#include "example.h"

Step 1b: Define Global Variables to Communicate with the Client Interface Objects

For single-threaded clients you have to declare in your main program the following global variables, used for communication with the interface objects: 

/* Needed global variables for the CLIENT interface object */
ERXCallId                 ERXCallId;
ERXeReturnCode            ERXrc;
ERX_ERROR_INFO            ERXErrorInfo;
ERX_Server_ADRESS         ERXServer;
ERX_CLIENT_IDENTIFICATION ERXClient;

Step 2: Required Settings for the C Wrapper

Step 2a: Identify the User with a Broker User ID

For implicit broker logon, if required in your environment, the client password can be given here. It is provided then through the interface object call. 

/* set client identification */
memset( &ERXClient, 0, sizeof(ERXClient) );
strcpy( (char*) ERXClient.szUserId, "ERX-USER" );
strcpy( (char*) ERXClient.szPassword, "ERX_PASS");

Step 2b: Set the Broker and Service to be Called

Your application will wait a maximum of 55 seconds for a server response. If the server does not answer within this period, the broker gives your program control again with an error code 00740074. 

ERXServer.Medium = ERX_TM_BROKER;
ERXServer.ulTimeOut = 55;

/* set Broker-Id, server-name, class-name and service-name */
strcpy( (char*) ERXServer.Address.BROKER.szEtbidName,   "ETB001" );
strcpy( (char*) ERXServer.Address.BROKER.szServerName,  "SRV1" );
strcpy( (char*) ERXServer.Address.BROKER.szClassName,   "RPC" );
strcpy( (char*) ERXServer.Address.BROKER.szServiceName, "CALLNAT" );

Step 3: Register with the RPC Runtime

As a general rule, before using the RPC runtime you have to register it. After registration, the RPC runtime holds information on a per-thread basis. See Using the RPC Runtime for more information. 

/* register to the RPC runtime */
ERXrc = ERXRegister( ERX_V81 );
If ( ERX_FAILED( ERXrc ) )
{
/* code for  error handling */
}

Step 4: Issue the RPC Request

The RPC interface object CALC is called as C function (see Calling Servers as Procedures or Functions). 

/* do the remote procedure call */
result = CALC( '+', 123456, 78910 );

Step 5: Examine the Error Code

When a return from the RPC request has been received, check whether the call was successful with the macro ERX_FAILED. 

if( ERX_FAILED( ERXrc ) )
{
/* code for error handling */
}

Detailed information about an error can be retrieved with the function ERXGetLastError. For the error messages returned, see Error Messages and Codes.

Step 6: Deregister with the RPC Runtime

As a general rule, after using the RPC runtime you should unregister from it. This will free all resources held by the RPC runtime for the caller. See Using the RPC Runtime for more information. 

/* unregister to the RPC runtime */
ERXUnregister();