The Qt OPC UA module implements a Qt API to interact with OPC UA on top of a 3rd party OPC UA stack.

The stacks are connected via plugins and can be selected/switched at runtime. Currently, the following implementations are supported

  • Open62541, MPLv2
  • Unified Automation C++ SDK (UACpp), Commercial
  • FreeOPCUA, LGPL v3

Getting started

Add the following line to your .pro file

QT += opcua

and include the Qt OPC UA headers into your files using

#include <QtOpcUa>

The examples demonstrate how to use Qt OPC UA API to interact with an OPC UA server.

A short introduction to OPC UA

OPC UA is a protocol for data modelling and exchange of data in industrial applications.

An OPC UA server offers access to data which is organized in a mesh of nodes connected by references. The use of different reference types and nodes containing metadata enable a client to navigate and interpret the data without knowing their structure in advance.

Each node has a unique identifier and attributes that can be read and written. Among others, there are Variable nodes which store values and callable Method nodes with attached nodes describing parameters and return values. Notifications in case of events and monitoring of Variable nodes for value changes are offered too.

Complex objects can be created by combining nodes using references, inheritance is also possible. OPC UA offers support for pre-made models which can be extended to fit special needs.

OPC UA is the platform-independent successor of OPC Classic intended for usage on all levels, from embedded sensors up to manufacturing execution and enterprise resource planning systems. It has a service-oriented architecture based on standardized messages for service requests and responses. There are different ways for these messages to be encoded and transported over the network. The most common way is binary encoding over TCP.

Implemented features from the OPC UA protocol

The following features of OPC UA are supported by Qt OPC UA:

FeatureOpen62541 pluginUACpp pluginFreeOPCUA plugin
Data change subscriptionsXXX
Modify subscriptions / monitored ItemsXX
Method callsXXX

Data types

A subset of the OPC UA data types is currently supported in Qt OPC UA. Most of them are available with all backends.

Data typeOpen62541 pluginUACpp pluginFreeOPCUA pluginQt OPC UA data type
Int16, Int32, Int64XXXDirectly used
UInt16, UInt32, UInt64XXXDirectly used
BooleanXXXDirectly used
DoubleXXXDirectly used
FloatXXXDirectly used

Classes and ownership

Two important classes are exposed to the user: QOpcUaClient and QOpcUaNode.

Objects of both classes are owned by the user and must be deleted when they are no longer needed.

Logging categories

The following logging categories are used by Qt OPC UA

Logging CategoryDescription
qt.opcuaPlugin independent messages generated by QOpcUaProvider and QOpcUaClient
qt.opcua.plugins.open62541Messages generated by the open62541 plugin
qt.opcua.plugins.uacppMessages generated by the UACpp plugin
qt.opcua.plugins.freeopcuaMessages generated by the freeopcua plugin

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