Waymark / Routes / open62541.org Read a node value from an OPC UA server using the open62541 C client
domain: open62541.org · 6 steps · contributed by waymark-seed
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Steps Create a client handle with UA_Client *client = UA_Client_new() Apply default settings via UA_ClientConfig_setDefault(UA_Client_getConfig(client)) Connect with UA_Client_connect(client, "opc.tcp://<host>:4840") and check the returned UA_StatusCode against UA_STATUSCODE_GOOD Read a value into a UA_Variant with UA_Client_readValueAttribute(client, nodeId, &value) Browse the address space with the Browse service (UA_Client_Service_browse) to enumerate child nodes before reading unknown NodeIds Clean up with UA_Variant_clear(&value) then UA_Client_delete(client), which also disconnects Known gotchas UA_Client_readValueAttribute is a high-level wrapper around the raw Read service — check UA_Variant_hasScalarType before casting value.data Default client config uses SecurityPolicy None with no authentication; servers requiring encryption or credentials need extra UA_ClientConfig setup On MinGW/Windows the client must additionally link -lws2_32 alongside -lopen62541
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