# Alternative to Union from Codesys **URL:** \ **Category:** Programming\ **Tags:** automation-studio, structured-text\ **Created:** [March 7, 2025, 8:49am UTC](https://community.br-automation.com/t/alternative-to-union-from-codesys/6150 "2025-03-07T08:49:19Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![Kili\_Theiler](https://avatars.discourse-cdn.com/v4/letter/k/FF8800/32.png) [@Kili\_Theiler](https://community.br-automation.com/u/Kili_Theiler)\ **Post date:** [March 7, 2025, 8:49am UTC](https://community.br-automation.com/t/alternative-to-union-from-codesys/6150/1 "2025-03-07T08:49:19Z")
Has B&R in Automation Studio with structured text something similar to Union from Codesys? ![Screenshot 2025-03-07 094236](https://europe1.discourse-cdn.com/brcommunity/original/2X/9/94b1d2ae4ff0f513d4c2eca94a026fdbba2800b4.png) ---
**Author:** ![alexander.hefner](https://dub1.discourse-cdn.com/brcommunity/user_avatar/community.br-automation.com/alexander.hefner/32/111_2.png) [@alexander.hefner](https://community.br-automation.com/u/alexander.hefner)\ **Post date:** [March 7, 2025, 9:39am UTC](https://community.br-automation.com/t/alternative-to-union-from-codesys/6150/2 "2025-03-07T09:39:58Z")
Hi, union is not supported right now (maybe with the release of ST OOP, which is coming with AS Code mid of this year). But if I got it right, it’s more or less a structure where the elements are aligned to the same size, right? So, if declaring a structure with for example 4 byte data types as elements only, it should have the same behavior as described … or I understood the explanation completely wrong, which is possible of course 😉 Best regards! ---
**Author:** ![christoph.hilchenbac](https://dub1.discourse-cdn.com/brcommunity/user_avatar/community.br-automation.com/christoph.hilchenbac/32/423_2.png) [@christoph.hilchenbac](https://community.br-automation.com/u/christoph.hilchenbac)\ **Post date:** [March 7, 2025, 10:57am UTC](https://community.br-automation.com/t/alternative-to-union-from-codesys/6150/3 "2025-03-07T10:57:16Z")
Hi, if the challenge is to save memory (e.g. a data base) one can simulate a union with a struct by storing also the data type and using dynamic variables to access the data. ```auto TYPE myRecordTypeEnum : ( REC_DINT, REC_REAL ); myRecord : STRUCT type : myRecordTypeEnum; data : ARRAY[0..3]OF USINT; END_STRUCT; END_TYPE ``` ```auto IF write_dint THEN write_dint := FALSE; ddint ACCESS ADR(record.data); record.type := REC_DINT; ddint := 3; END_IF IF write_real THEN write_real := FALSE; dreal ACCESS ADR(record.data); record.type := REC_REAL; dreal := 3.1415; END_IF IF read THEN read := FALSE; CASE record.type OF REC_DINT: ddint ACCESS ADR(record.data); (* do something with ddint *) REC_REAL: dreal ACCESS ADR(record.data); (* do something with dreal *) ELSE (* invalid datatype *) END_CASE END_IF ``` ```auto VAR dreal : REFERENCE TO REAL; ddint : REFERENCE TO DINT; record : myRecord; write_dint : BOOL; write_real : BOOL; read : BOOL; END_VAR ``` ---
**Author:** ![Matt\_Buck](https://avatars.discourse-cdn.com/v4/letter/m/FF8800/32.png) [@Matt\_Buck](https://community.br-automation.com/u/Matt_Buck)\ **Post date:** [March 7, 2025, 4:25pm UTC](https://community.br-automation.com/t/alternative-to-union-from-codesys/6150/4 "2025-03-07T16:25:05Z")
Not currently as I don’t believe it’s a part of the IEC 61131 main standard. Per this blog post [IEC 61131-3: Additional language extensions – Stefan Henneken](https://stefanhenneken.net/2017/06/17/iec-61131-3-additional-language-extensions/), twin cat and codesys may support it in some fashion, and per Alex, it might be supported in ST OOP in Automation Studio Code. But currently it isn’t a part of the structured text language as implemented in Automation Studio. Automation Studio’s compliance with the IEC 61131-3 standard is documented in the AS help [B&R Online Help](https://help.br-automation.com/#/en/4/programming%2Fprogrammingmodel_compliancelist.html). I don’t see it listed as part of the standard. You may be able to implement something in a library in C to handle this and then wrap it up nicely for structure text usage. For other’s not familiar, a union defines multiple ways to access the same memory address with different formats. i.e. I can define a UNION of BYTE[4] and a DWORD and then be able to access each of the bytes of the DWORD via the BYTE array without having to do any ACCESS or memcpy(). (It’s a commonly used in C and other languages, but from what I can tell not a part of the 61131-3 standard, edition 3.) ---
**Author:** ![Swee\_Hoe](https://avatars.discourse-cdn.com/v4/letter/s/FF8800/32.png) [@Swee\_Hoe](https://community.br-automation.com/u/Swee_Hoe)\ **Post date:** [March 10, 2025, 4:12am UTC](https://community.br-automation.com/t/alternative-to-union-from-codesys/6150/5 "2025-03-10T04:12:09Z")
Finally I see someone question about structured text implementation in Automation Studio. 🙂 I not sure `UNION` is covered in 61131-3: 2013 but I will say that it is better to have it. Secondly, I think 61131-3 did covered OOP but ST in B&R Automation Studio does not have it. I glad to hear that we will get it soon(ST OOP). ---
**Author:** ![Kili\_Theiler](https://avatars.discourse-cdn.com/v4/letter/k/FF8800/32.png) [@Kili\_Theiler](https://community.br-automation.com/u/Kili_Theiler)\ **Post date:** [March 10, 2025, 7:52am UTC](https://community.br-automation.com/t/alternative-to-union-from-codesys/6150/6 "2025-03-10T07:52:34Z")
Thank you for all the replies. I use union mostly for conversions, for example, Modbus registers (status and control words) and PLC internal flags. I think Matt Buck’s approach with the C function will help me. ---
**Author:** ![christoph.hilchenbac](https://dub1.discourse-cdn.com/brcommunity/user_avatar/community.br-automation.com/christoph.hilchenbac/32/423_2.png) [@christoph.hilchenbac](https://community.br-automation.com/u/christoph.hilchenbac)\ **Post date:** [March 12, 2025, 7:21am UTC](https://community.br-automation.com/t/alternative-to-union-from-codesys/6150/7 "2025-03-12T07:21:02Z")
> [@Kili\_Theiler](#): > > I use union mostly for conversions this is called ‘type-punning’ and there is a nice article on stackoverflow about it: > TLDR: Using Unions for “type punning” is fine in C, and fine in gcc’s C++ as well (as a gcc [g++] extension). But, “type punning” via unions has hardware architecture _endianness considerations_