open62541/examples/tutorial_client_firststeps.c

/* This work is licensed under a Creative Commons CCZero 1.0 Universal License.
 * See http://creativecommons.org/publicdomain/zero/1.0/ for more information. */

/**
 * Building a Simple Client
 * ------------------------
 * You should already have a basic server from the previous tutorials. open62541
 * provides both a server- and clientside API, so creating a client is as easy as
 * creating a server. Copy the following into a file `myClient.c`: */

#include <stdio.h>
#include "open62541.h"

int main(void) {
    UA_Client *client = UA_Client_new(UA_ClientConfig_standard);
    UA_StatusCode retval = UA_Client_connect(client, "opc.tcp://localhost:4840");
    if(retval != UA_STATUSCODE_GOOD) {
        UA_Client_delete(client);
        return (int)retval;
    }

    /* Read the value attribute of the node. UA_Client_readValueAttribute is a
     * wrapper for the raw read service available as UA_Client_Service_read. */
    UA_Variant value; /* Variants can hold scalar values and arrays of any type */
    UA_Variant_init(&value);

    /* NodeId of the variable holding the current time */
    const UA_NodeId nodeId =
        UA_NODEID_NUMERIC(0, UA_NS0ID_SERVER_SERVERSTATUS_CURRENTTIME);

    retval = UA_Client_readValueAttribute(client, nodeId, &value);
    if(retval == UA_STATUSCODE_GOOD &&
       UA_Variant_hasScalarType(&value, &UA_TYPES[UA_TYPES_DATETIME])) {
        UA_DateTime raw_date = *(UA_DateTime*)value.data;
        UA_String string_date = UA_DateTime_toString(raw_date);
        printf("string date is: %.*s\n", (int)string_date.length, string_date.data);
        UA_String_deleteMembers(&string_date);
    }

    /* Clean up */
    UA_Variant_deleteMembers(&value);
    UA_Client_delete(client); /* Disconnects the client internally */
    return UA_STATUSCODE_GOOD;
}

/**
 * Compilation is similar to the server example.
 *
 * .. code-block:: bash
 *
 *     $ gcc -std=c99 open6251.c myClient.c -o myClient
 *
 * Further tasks
 * ^^^^^^^^^^^^^
 *
 * - Try to connect to some other OPC UA server by changing
 *   ``opc.tcp://localhost:16664`` to an appropriate address (remember that the
 *   queried node is contained in any OPC UA server).
 *
 * - Try to set the value of the variable node (ns=1,i="the.answer") containing
 *   an ``Int32`` from the example server (which is built in
 *   :doc:`tutorial_server_firststeps`) using "UA_Client_write" function. The
 *   example server needs some more modifications, i.e., changing request types.
 *   The answer can be found in "examples/exampleClient.c". */