Incorrect/Unexpected POU Path Initialization

2020-11-12T05:58:26.645000Z

Example Project

Incorrect/Unexpected POU Path Initialization

2020-11-12T05:56:04.712000Z

I created a function block to initialize its Path string variable to the function block's path using the appropriate attribute pragmas as shown below. An instance of this function block in the main program is initialized to the correct and expected path.

{attribute 'reflection'}
FUNCTION_BLOCK PathTestFunctionFB 

VAR
    {attribute 'instance-path'}
    {attribute 'noinit'}
    Path        : STRING(255);
END_VAR

I created a second function block in the same manner that also contains an instance of the first. An instance of this block, in the main program, and its instance of the first block are initialized correctly and as expected.

{attribute 'reflection'}
FUNCTION_BLOCK PathTestBaseFB
VAR_INPUT
    PathTestFunction    : PathTestFunctionFB;
END_VAR

VAR
    {attribute 'instance-path'}
    {attribute 'noinit'}
    Path        : STRING(255);
END_VAR

I created a third function block which extends the second block as shown below. This block does not contain attribute pragmas or variable declarations. Instead, it inherits everything from the second function block. An instance of this block in the main program initializes both inherited path variables for Base and Function function blocks to the same value, which seems to be incorrect or at least unexpected.

FUNCTION_BLOCK PathTestDerivedFB EXTENDS PathTestBaseFB

An example project and screen shot of the initialized path variables are attached.

[[PathTest.png]]

Recent posts to Incorrect/Unexpected POU Path Initialization

Incorrect/Unexpected POU Path Initialization

Incorrect/Unexpected POU Path Initialization