open62541 and HOLDING_REGISTR

[Акакий Бездрищенко]

Hello guys! I'm trying to read tags from MasterOPC using the open62541 C library in Visual Studio. Here's how:

  int main(void)

 { 

   UA_Client *client = UA_Client_new();       UA_ClientConfig_setDefault(UA_Client_getConfig(client));

 const char *endpoint = "opc.tcp://localhost:4840";

 UA_StatusCode retval = UA_Client_connect(client, endpoint);

 if(retval != UA_STATUSCODE_GOOD)

 {

 printf("Failed to connect: %s (0x%08x)\n", UA_StatusCode_name(retval), retval); UA_Client_delete(client); 

return (int)retval;

 } 

printf("Connected to %s\n", endpoint);

 UA_NodeId nodeId = UA_NODEID_STRING(1, "Channel1.Device1.TagName"); 

UA_Variant value; UA_Variant_init(&value); 

retval = UA_Client_readValueAttribute(client, nodeId, &value);

 if(retval == UA_STATUSCODE_GOOD)

 { 

// Check the type and print the value

 if(UA_Variant_hasScalarType(&value, &UA_TYPES[UA_TYPES_FLOAT]))

 { 

float val = *(float*)value.data; printf("Value (Float): %.3f\n", val);

 } 

else

 if(UA_Variant_hasScalarType(&value, &UA_TYPES[UA_TYPES_INT32]))

 { 

UA_Int32 val = *(UA_Int32*)value.data; 

printf("Value (Int32): %d\n", (int)val);

 } 

else

 if(UA_Variant_hasScalarType(&value, &UA_TYPES[UA_TYPES_BOOLEAN]))

 { 

UA_Boolean val = *(UA_Boolean*)value.data; printf("Value (Bool): %s\n", val ? "true" : "false");

 } 

else

 if(UA_Variant_hasScalarType(&value, &UA_TYPES[UA_TYPES_STRING]))

 { 

UA_String str = *(UA_String*)value.data; printf("Value (String): %.*s\n", (int)str.length, str.data);

 } 

else

 { printf("Value of another type (not processed)\n");

 } 

} 

else

 { 

printf("Read error: %s (0x%08x)\n", UA_StatusCode_name(retval), retval);

 } 

UA_Variant_clear(&value); UA_Client_disconnect(client); UA_Client_delete(client); printf("\nDone. Press Enter...\n"); getchar(); return 0;

 } 

I inserted the server IP, port, and nodeI. And here's the problem: Tags like SERVER_ONLY are read correctly, but other types, like HOLDING_REGISTR, aren't read at all. What could be wrong, please tell me. Grock insists that the ns value might be incorrect, but I'm checking it in UaExpert. And just to be sure, I tried reading in a loop, iterating through ns values ​​from 0 to 32. It didn't work. Please help a noob.

[Jacky Bek]

what is the error code return from

1. UA_Client_connect()

2. UA_Client_readValueAttribute()

Sent from my iPhone

On 3 Feb 2026, at 03:37, Акакий Бездрищенко <bezdri...@gmail.com> wrote:



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