Does pointer to struct and pointer in struct exist in SCL?!?!?

I'm trying to create a ring buffer and got two problems with pointers:

First, Inmy C-code I'm trying to translate to SCL I have the following struct:
[code]struct ringBuff_t
{
int head;
int tail;
int items;
int elemSize;
char *data;
}[/code];
But how do I make a char pointer in SCL?
(as there is no dynamic memory my plan is to use a variable allocated in some DB that is loaded into the data pointer at startup in an init function, this to make it possible to use same ring buffer functions for different data types as I'm using several ring buffers with differently sized data)

The second problem is how to pass the pointer to my ringBuff_t when calling the functions. When just putting a variable of type ringBuff_t in the VAR_IN_OUT section I get problems when passing on the object to lower layers I get an error 15:16499 when trying to use more than one call layer (I've got a parser function with the buffer as input, it can not call my buffer functions without making a local copy of that buffer). So how to I create a pointer to a UDT that I can use to refer to my buffer in several layers offunction calls?

One way of storing pointers in struct might be to use ANY type, but as ANY can't be stored in a struct I could define my own copy of the ANY-pointer struct and copy the contents of the ANY input variable address data indirectly using DB number and the byte index, or am I missing something? Is there maybe a reason why ANY pointers can't be stored, are not pointers valid in all cases?

Using the ANY type might also be the solution to input a pointer to a struct, but if I have an ANY pointer how do I convert it back to my datatype to access my data?, is it possible to create a view using the AT keyword or do I need to index my struct byte by byte by adding constants to the base address?

Hi, I have a question regarding this thread.

Mr. Smiffy, you have explained very well how to use pointer to specific data type in structure (creating disassembled ANY pointer and so on). I already use this solution in my project, and for that i thank you very much.

The question that I have regarding usage of pointer to struct in some other structure, so

Struct1: Struct

   var1:bool;

   var2:int;

   var3 : pointer to struct2; (???)

end_struct;

Struct2: Struct

   var:bool;

   ...

end_struct;

 Is it possible to do so?

Best regards,

Janko

Hi Smiffy, 

thank you very much for clearing all doubts!

Janko

Hi Smiffy,

I think that I might have found the solution for pointer to struct. 

FUNCTION_BLOCK "FB_Prova"

{ S7_Optimized_Access := 'FALSE' }

AUTHOR : Janko

VERSION : 0.1

   VAR 

      Struttura : Struct

         var1 : Word;

         var2 : Int;

      END_STRUCT;

      Struttura_1 : Struct

         var1 : Word;

         var2 : Int;

      END_STRUCT;

      i { S7_HMI_Visible := 'False'} : Int;

      Address { S7_HMI_Visible := 'False'} : Array [0 .. 1] of Word;

      Address_1 { S7_HMI_Visible := 'False'} : Array [0 .. 1] of Word;

   END_VAR

   VAR_TEMP 

      pAnyStruct : Struct

         S7Code : Byte;

         DataType : Byte;

         Lenght : Int;

         DBNumber : Int;

         MemoryArea : Byte;

         ByteAddressMSB : Byte;

         ByteAddressLSB : Word;

      END_STRUCT;

      pAny AT pAnyStruct : Any;

      DataType_Array : Array[0..1] of Byte;

      pAnyStruct_1 : Struct

         S7Code : Byte;

         DataType : Byte;

         Lenght : Int;

         DBNumber : Int;

         MemoryArea : Byte;

         ByteAddressMSB : Byte;

         ByteAddressLSB : Word;

      END_STRUCT;

      pAny_1 AT pAnyStruct_1 : Any;

      DataType_Array_1 : Array[0..1] of Byte;

      RetVal : Int;

   END_VAR

BEGIN

#DataType_Array[0] := 16#04;

#DataType_Array[1] := 16#05;

#Address[0] := 2#0000000000000000;

#Address[1] := 2#0000000000010000;

#Address_1[0] := 2#0000000000100000;

#Address_1[1] := 2#0000000000110000;

#DataType_Array_1[0] := 16#04;

#DataType_Array_1[1] := 16#05;

FOR #i := 0 TO 1 BY 1 DO

 

 #pAnyStruct.S7Code := 16#10;

 #pAnyStruct.DataType := #DataType_Array[#i];

 #pAnyStruct.Lenght := 1;

 #pAnyStruct.DBNumber := 1;

 #pAnyStruct.MemoryArea := 16#85;

 #pAnyStruct.ByteAddressMSB := 0;

 #pAnyStruct.ByteAddressLSB := #Address[#i];

 #pAnyStruct_1.S7Code := 16#10;

 #pAnyStruct_1.DataType := #DataType_Array[#i];

 #pAnyStruct_1.Lenght := 1;

 #pAnyStruct_1.DBNumber := 1;

 #pAnyStruct_1.MemoryArea := 16#85;

 #pAnyStruct_1.ByteAddressMSB := 0;

 #pAnyStruct_1.ByteAddressLSB := #Address_1[#i];

 

 #RetVal := BLKMOV(SRCBLK := #pAny, DSTBLK => #pAny_1);

 

END_FOR;

END_FUNCTION_BLOCK

I'd like to see you're prospective on it. Have you tried something similar? Any suggestions?

Best regards,

Janko