Originally created by: Captive Engineer

Hello.

I am struggling to understand the CheckPointer function in CoDeSys. The help file says that if I include a function that is exactly named "CheckPointer", the function shall "be called automatically before each access on the address of a pointer." This statement suggests that I do not have to make an explicit call to the function, but if I don't call the function, I do not understand how to obtain the result of the implicit function call. So I start with two questions:

1) How do I obtain the DWORD result of the CheckPointer function call?
2) What is the result indication for a valid memory versus an invalid memory location?

The function declaration looks like this:

FUNCTION CheckPointer : DWORD
VAR_INPUT
   dwAddress   :   DWORD;
   iSize      :   DINT;
   bWrite      :   BOOL;
END_VAR

I am using a 32-bit system.

This brings me to my third question. The help file does not indicate any code for the CheckPointer function, just its interface declaration.

3) Do I need to add any code into the actual CheckPointer function?

If the answer to question #3 is that no code needs to be added, then how is the CheckPointer function actually testing anything?

Finally, is there any example code that illustrates the proper use of this CheckPointer function? The help file does not seem to go any further than describing the input interface, but this is no illustration of how to use it.

Thank you for whatever explanations you can provide.

Kind regards,
The Captive Engineer