STRUCT_BLOCK

A STRUCT_BLOCK is a user-defined composite type. Struct blocks are an extremely useful facility to group variables as in this example:

STRUCT_BLOCK sbBufferPDU
   length : INT;
   data   : ARRAY[1..140} OF SINT;
END_STRUCT_BLOCK;

The biggest advantage of the STRUCT_BLOCK is found when writing data of different types to the serial port, PDU message, or file system.

Instead of writing the data types individually, they can be grouped in a STRUCT_BLOCK, and the device sees it as one variable.

STRUCT_BLOCK sbGpsData
   mode         : SINT;
   linsec       : DINT;
   latitude     : DINT;
   longitude    : DINT;
   speed        : DINT;
   course       : DINT;
   height       : INT;
   PDOP         : INT;
   HDOP         : INT;
   VDOP         : INT;
   inview       : SINT;
   used         : SINT;
END_STRUCT_BLOCK;
 
VAR
   gpsData : sbGpsData; 
END_VAR;

To access the members of a STRUCT_BLOCK, the same syntax as used with a FUNCTION_BLOCK is used.

For example:

gpsData.speed := 100;

 
STRUCT_BLOCK assignment

A complete STRUCT_BLOCK value can be assigned to another variable with the := operator. The source and destination must be declared with the exact same STRUCT_BLOCK type.

The assignment copies all members, including elementary values, STRING values, nested STRUCT_BLOCK values, arrays, arrays of STRING, and arrays of STRUCT_BLOCK. STRING members use normal STRING assignment semantics, including automatic reference management.

STRUCT_BLOCK position;
 value : DINT;
 text : STRING;
END_STRUCT_BLOCK;
 
STRUCT_BLOCK record;
 title : STRING;
 location : position;
 values : ARRAY[0..9] OF INT;
 names : ARRAY[0..2] OF STRING;
 positions : ARRAY[0..1] OF position;
END_STRUCT_BLOCK;
 
VAR
 source, destination : record;
 list1, list2 : ARRAY[0..3] OF record;
 i, j : INT;
END_VAR;
 
destination := source;
list2[i] := list1[j];
destination.location := source.location;

Restrictions:

•Separately declared STRUCT_BLOCK types are incompatible even when their members have identical types and layout.

•Individual ARRAY OF STRUCT_BLOCK elements can be assigned. Complete standalone ARRAY variables cannot be assigned.

•FUNCTION_BLOCK and THREAD_BLOCK instances cannot be assigned.

•A FUNCTION cannot return a STRUCT_BLOCK value directly. Use ACCESS STRUCT_BLOCK parameters when a function must produce a composite result.

•Self-assignment, for example item := item, is permitted.

To send the data through a serial channel:

serSendData(port:=1, data:=ADDR(gpsData), size:=SIZEOF(gpsData));  

Note: STRUCT_BLOCK assignment handles STRING members safely using normal STRING assignment semantics. Raw memory operations are different: a STRING member stored inside a STRUCT_BLOCK contains a string handle, not the character data. Sending or storing a STRUCT_BLOCK using ADDR and SIZEOF therefore does not serialize the contents of its STRING members.