Codesys 3.5, STRUCT and UNION

[leon78]

I declare a structure:

TYPE sdoName:
STRUCT
    i1: INT;
    i2: INT;  
END_STRUCT
END_TYPE

I declare a UNION:

TYPE uName:
UNION
    di : DINT;
    n : sdoName;
END_UNION
END_TYPE

I declare a variable:

VAR
	v: uName;
END VAR

Now I can access variable fields:

diX := v.di;
iX1 := v.n.i1; 
iX2 := v.n.i2;

But I want do it without "n":

diX := v.di;
iX1 := v.i1; 
iX2 := v.i2;

How I can declarate UNION for it? I thought:

TYPE uName:
UNION
    di : DINT;
   STRUCT
    i1: INT;
    i2: INT;  
   END_STRUCT
END_UNION
END_TYPE

But it is wrong.

 

[Peter Nachtwey]

I declare a structure:

TYPE sdoName:
STRUCT
    i1: INT;
    i2: INT;  
END_STRUCT
END_TYPE

I declare a UNION:

TYPE uName:
UNION
    di : DINT;
    n : sdoName;
END_UNION
END_TYPE

I declare a variable:

VAR
	v: uName;
END VAR

Now I can access variable fields:

diX := v.di;
iX1 := v.n.i1; 
iX2 := v.n.i2;

But I want do it without "n":

diX := v.di;
iX1 := v.i1; 
iX2 := v.i2;

How I can declarate UNION for it? I thought:

TYPE uName:
UNION
    di : DINT;
   STRUCT
    i1: INT;
    i2: INT;  
   END_STRUCT
END_UNION
END_TYPE

But it is wrong.

Yes, You should be able to do what you want to do but what you are doing is not right. How would access i2?

I think you will have better luck if you define the structure out side of the union as its own type then include that type in the union or giving the structure a name so you can specify the structure type so the compiler will know the offset of the i2 within the structure.

 

[kalabdel]

Use inheritance.
Type uName EXTENDS sdoName

 

[leon78]

Use inheritance.
Type uName EXTENDS sdoName

Thank you, but it does not work as a UNION

 

[drbitboy]

From scoping considerations, it should not be possible.


Consider the following:

 TYPE sdoName:
   STRUCT
     [COLOR=Red][B]i1[/B][/COLOR]:    INT;
     i2:    INT;
   END_STRUCT
END_TYPE

Then

 TYPE uName:
  UNION
    [COLOR=red][B]i1[/B][/COLOR] : DINT;
    n  : sdoName;
  END_UNION
END_TYPE

Then

VAR
   v: uName;
END VAR

If we could refer to the struct v.n's members without the intervening .n, then how could the code distinguish between v.n.i1 and v.i1?

 

[kalabdel]

Interesting! And it turns out to be an old problem ( I didn't read the whole thing) and not limited with CodeSys.

I think it has to do with memory allocation.

I am not sure why the compiler only produces a warning when the result is such a mess.


Edit: More to come............ I am testing it and I think it works quite well.

 

[kalabdel]

It appears to work well; see this .gif.


The the members of a UNION share the same memory and so only one member can be use at a time. You can see that from the memory address of the UNION members and compare that to the local variables with each have a separate memory area allocated to them.


Was that what you wanted to achieve?

 

[leon78]

Please, show me declarations for uName and sdoName

 

[drbitboy]

Cool! di is supposed to be a DINT, according to OP, but it should work the same.


What happens if you use the name [i1] or [i2] for the name of the variable with the name [di] now?

 

[drbitboy]

With di as a DINT, try inserting the following ELSIFs before the END_IF, and the following TON after the END_IF:

ELSIF doRollover THEN

     v.di := 65535;

ELSIF timer.Q THEN

     v.di := v.i1 + 1;

     doRollover := FALSE;

END_IF;



TON(timer,IN=doRollover,PT=T#5s);

​

 

[leon78]

It appears to work well; see this .gif.

Why do you have same address for v.i1 and v.di?

My code:

TYPE sdoName :
STRUCT
    i1: INT;
    i2: INT; 
END_STRUCT
END_TYPE

TYPE uName EXTENDS sdoName :
STRUCT
	di : DINT;
END_STRUCT
END_TYPE

PROGRAM prgLogic1
VAR
	test: uName;
	i1Address: POINTER TO INT;
	i2Address: POINTER TO INT;
	diAddress: POINTER TO DINT;
END_VAR

i1Address := ADR (test.i1);
i2Address := ADR (test.i2);
diAddress := ADR (test.di);

 

[leon78]

I got it!

TYPE uName EXTENDS sdoName :
UNION
	di : DINT;
END_UNION
END_TYPE

Thank you very much!

 

[JeremyM]

If there's a sizeof() instruction available, how many bytes does that object consume?

 

[kalabdel]

Sorry drbitboy abd Jeremy and good catch. I declared "diX" and " v.di" in (uName) as INT not DINT.

 

[kalabdel]

Here's another interesting one.