How to get the pointer to the address of a struct in a struct?

Morning,
I would like to get the pointer to the address of a strcut in a struct, In my case, the struct is called ST_Control_PP08.CodigoEstado, so, I thought that L P##"ST_Control_PP08".CodigoEstado will work, but it didnt work. So, is there any posibility?

I have programmed a "solution" but I would like not use P#40.0, instead of that I would like to load in ar1 directly the correct address

Hi,

I know is not the answer you are looking for...but...how about switching to access symbolically? Are you on S71500 hardware platform?

What if you use UDT instead of simple Structs?

Hi alvconsan,

Maybe a solution, if you only need to read elements, could be copy the substruct to a temporal struct (with the same elements and length).  And Access or work directly with this temporal.

alvconsan

but I was looking something like get the pointer directly to the struct in the struct

You can use  +AR1 P#40.0 in your example to achieve this (after loading the original pointer into AR1) and this may/would have the advantage that only one line of code needs to be adjusted should you make changes to the STAT area).

A word of caution too: FB's are by default Multi-Instance capable and AR2 contains the Multi-Instance offset. You MUST consider the AR2 based offset if you do call your FB as a Multi-Instance, but it of course doesn't hurt to generally consider the AR2 for this (more so if this is a reusable FB and will be used in future project where someone may want to multi instantiate it)  

Have a look at the bottom of https://support.industry.siemens.com/cs/us/en/view/20443243 for how to include the AR2 based multi Instance offset

alvconsan

I have been doing some tests about the last task, I have observed that at first ar2 is 16#8400_0000. But I thought that if I get the address of the first variable of my FB ( in my case an Input) I got a 16#8500_0000, so, it confused me, becasuse I thought I will get the same. Even more, I tried too to get acces to Temp area in the DB and the value is 16#8600_0000. This last thing make me think that it is a relation between the different areas of the FB's DB and the first value of ar2. Do you know something about? thank you very much. :)

Hi alvcosan

What you are seeing is all correct and has to do with the memory area that is part of a pointer and attached is a pdf from the Step7 inbuilt help with more on this.

In short though, TAR2 will get you 84xx_xxxx as it is the (Instance) DB of the calling FB that you are accessing. This is why you do an "AD DW#16#00FF_FFFF" before adding it to your AR1 Pointer to get rid of the DB "84" memory area.

Any Pointer loading to the FB's IN, OUT, IN_OUT or STAT area will be an 85xx_xxxx as it is Instance DB data (irrespective of the actual variable that is assigned to IN, OUT or IN_OUT as their value is stored in the FB's IDB from which you access it, aka "pass by value").  

Lastly, any Pointer loading to TEMP variables will be an 86xx_xxxx.