An important part of OOP is to use access specifiers to make member methods and variables inaccessible from outside of the object.
When declaring a function block method is is easy to control the Access Specifier, but I have not found a way to control access to member variables.

Is it possible and if yes, how?

CodePudding user response：

Every variable that you declare under the VAR section of your Function Block is considered private.

There is no public or private keyword for variables in IEC 61131-3

Another thing you can do if you absolutely want to use public/private keywords is to define properties.

CodePudding user response：

You can actually still access internal variables of an object direcly in code (no pointers), but they are read only. The code completion will not display the internal variables though, but after you finish typing the name structure, you will see no compile errorrs - test := fb1.internalVariable will be a valid read action actually while fb1.internalVariable := 5; will end up giving you an error, saying that the variable is not an input to the function block (or any other object for that matter).