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`: .. code-block:: c #include #include #include int main(void) { UA_Client *client = UA_Client_new(); UA_ClientConfig_setDefault(UA_Client_getConfig(client)); UA_StatusCode retval = UA_Client_connect(client, "opc.tcp://localhost:4840"); if(retval != UA_STATUSCODE_GOOD) { UA_LOG_INFO(UA_Log_Stdout, UA_LOGCATEGORY_USERLAND, "The connection failed with status code %s", UA_StatusCode_name(retval)); UA_Client_delete(client); return 0; } /* 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_DateTimeStruct dts = UA_DateTime_toStruct(raw_date); UA_LOG_INFO(UA_Log_Stdout, UA_LOGCATEGORY_USERLAND, "date is: %u-%u-%u %u:%u:%u.%03u", dts.day, dts.month, dts.year, dts.hour, dts.min, dts.sec, dts.milliSec); } else { UA_LOG_INFO(UA_Log_Stdout, UA_LOGCATEGORY_USERLAND, "Reading the value failed with status code %s", UA_StatusCode_name(retval)); } /* Clean up */ UA_Variant_clear(&value); UA_Client_delete(client); /* Disconnects the client internally */ return 0; } Compilation is similar to the server example. .. code-block:: bash $ gcc -std=c99 myClient.c -lopen62541 -o myClient In a MinGW environment, the Winsock library must be added. .. code-block:: bash $ gcc -std=c99 myClient.c -lopen62541 -lws2_32 -o myClient.exe Further tasks ^^^^^^^^^^^^^ - Try to connect to some other OPC UA server by changing ``opc.tcp://localhost:4840`` 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/client.c``.