Feature: read a struct of struct

[kbonnot]

At the moment, reading a struct value is possible thanks to 'read_structure_by_name', but it doesn't work for struct composed of structs:

I've tried adding this through a recursive function

(my modification is l267), the num_of_bytes is correct, but the function for reading it can't cope.

It would be a greatly useful feature !

Thanks in advance

[chrisbeardy]

There is a workaround for this if you define your structure in python with the other structure embedded: eg

TYPE test1 :
STRUCT
    bTest1 : BOOL;
    bTest2 : BOOL;
    bTestStruct : test2;
END_STRUCT
END_TYPE

TYPE test2 :
STRUCT
    bTest3 : BOOL;
    bTest4 : BOOL;
END_STRUCT
END_TYPE

TEST_STRUCTURE_1: pyads.StructureDef = (
    ("bTest1", pyads.PLCTYPE_BOOL, 1),
    ("bTest2", pyads.PLCTYPE_BOOL, 1),
    ("bTestStruct.bTest3", pyads.PLCTYPE_BOOL, 1),
    ("bTestStruct.bTest4", pyads.PLCTYPE_BOOL, 1),

I have made a function which helps you combine two structures.

def _amend_def_var(var, original_def: pyads.StructureDef) -> pyads.StructureDef:
    return tuple(((var + "." + i[0]),) + tuple(i[1:]) for i in original_def)

Unfortuantly there is no PLC_TYPE for a structure or way to recognise something is a structure using ADS, which means the read_structure_by_name is a "hack" which just converts a stream of bytes, we may be able to manipulate the function so you pass a list of structure definitions into the function then it could look up if no PLC type is there a matching definition passed to it that it can use for recursion.

[tboegi]

...PLC_TYPE for a structure or way to recognise something is a structure using ADS

There is a definition: search for something call BIGTYPE (or similar) See here, it is defined as 65: https://infosys.beckhoff.com/english.php?content=../content/1033/tcadsocx/12466639883.html&id=

However, I don't have a good pointer to "decode" the "bigtype" into the members of a struct. But it should be possible, since TwinCAT.exe itself is able to do so. More digging needed

[FilipeJSRosa]

Any update on this item? Still not possible to read a struct of struct without declaring them on python?

[chrisbeardy]

The best update I can give is that this feature is not actively being worked on. This is a project run by volunteers so unfortunately development often happens in stints when the time allows. If you are familiar with python and twincat please feel free to submit a PR. Thanks