In the previous article (here), we explained the overview of OPC-UA and how to install Open62541.
Please take a look before reading this article.

In this article, we will explain the following items:

• Creating an OPC-UA Client sample
• Reading and writing variables registered on the server
• Calling functions registered on the server

For development, we use the following libraries and tools:

• Visual Studio
  • This article uses Visual Studio 2022 Community
• OpenSSL
  • This article uses OpenSSL 3.0.7
• CMake
  • This article uses CMake 3.25.0-rc2
• Python3
  • This article uses Python 3.12.0
• UaExpert
  • OPC-UA client tool
  • Used to check the values registered on the server

We will explain how to create and configure a project for the OPC-UA client.

Open Visual Studio and open the "open62541_ws" solution.
From the top left tab, select "File" → "New" → "Project".

Select "Console App" for C++.

Configure the project as follows:
The project will be created inside the src folder.

Project name: SimpleClient
Location: <Solution Directory>/src
Solution: Add to the solution

To make development easier in Visual Studio, configure the project.
Right-click "SimpleClient" in the Solution Explorer and select properties.

Configure the project settings on this screen.

Set "Configuration" at the top of the SimpleClient property page to "All Configurations".

From the left "Configuration Properties" column,

Select "Configuration Properties" → "C/C++" → "General".

In the right column, set "Additional Include Directories" to

$(SolutionDir)include

Click "Apply" after setting.

From the left column,

Select "Configuration Properties" → "Linker" → "General".

In "Additional Library Directories", set

$(SolutionDir)lib

Click "Apply" after setting.

From the left column,

Select "Configuration Properties" → "Linker" → "Input".

In "Additional Dependencies", append

$(SolutionDir)lib\open62541.lib

The separator for setting values here is a semicolon.

Click "Apply" after setting.

From the left column,

Select "Configuration Properties" → "General".

Next to "Output Directory", click the triangle icon and click the "Edit..." button to open the edit screen.

Set as follows:

$(SolutionDir)bin\$(ProjectName)\$(Configuration)\

Click "Apply" after setting.

When executing the program after building, it is necessary to link open62541.dll at the application startup.

Here, we set to copy the dll file to the output directory after building.

From the left column,

Select "Configuration Properties" → "Build Events" → "Post-Build Event".

Enter the following 2 lines in "Command Line":

robocopy $(SolutionDir)bin\ $(TargetDir) open62541.dll
IF %ERRORLEVEL% LSS 8 EXIT 0

The second line is a command to suppress errors that occur when the robocopy command is successful.
For more details, see here.

Click OK to close the property screen after setting.

This completes the project configuration.

In the previous article, we registered the following two nodes on the server:

• An integer variable SampleVariable
• A function IncreaseVariable(int delta) that adds the value of the argument to SampleVariable

We will implement a client that accesses these two nodes in this article.

Write the following code inside the created SimpleClient.cpp.
The code implemented in this article is also posted here.

[Code omitted for brevity, please refer to the original article for the full code]

[Explanation of the code for reading a variable's value]

[Explanation of the code for writing a value to a variable]

[Explanation of the code for executing a function]

[Explanation of the main function]

• Launch the OPC-UA server created in the previous article
• Start UaExpert and connect to the OPC-UA server
• Store any value in SampleVariable
  • This time, it was changed to 100

Launch the created client and confirm that the screen like the one below is displayed.
[Client launch screen]

Press the Enter key and read the current value of the variable.
As a result of the execution, confirm that it has become the value changed earlier.
[Client after reading the variable]

Press the Enter key again, and try to change the value of the variable.
As a result of the execution, confirm that the value has become the value written in the code (-1).
[Client after writing the variable]

Finally, press the Enter key again and try to execute the function on the server.
Here, the contents of the function were written to add the value passed as an argument (this time 32).
As a result of the execution, confirm that the value has become the correct value (-1 + 32 = 31).
[Client after invoking the method]

This article did not introduce it, but Open62541 provides features such as encryption and PubSub communication, and samples are published on the official GitHub repository.
Why not try using Open62541 for OPC-UA server and client development?
Open62541 sample program collection

open62541pp