The following functions enable the dynamic allocation of arrays for storing DINT integer values:

ARCREATE allocates an array of DINT integers.
ARREAD read a DINT integer in an array allocated by ARCREATE.
ARWRITE write a DINT integer in an array allocated by ARCREATE.

attentionAttention
  • The memory used for those arrays is allocated directly by the Operating System of the target. There is no insurance that the required memory space will be available.
  • Allocating large arrays may cause the Operating System to be instable or slow down the performances of the target system.
  • Dynamic memory allocation may be unsuccessful (not enough memory available on the target). Your application should process such error cases in a safe way.
  • Dynamic memory allocation may be not available on some targets. Please refer to OEM instructions for further details about available features.

ARCREATE: array allocation

OK := ARCREATE (ID, SIZE);

ID : DINT  integer ID to be assigned to the array (first possible ID is 0) .
SIZE : DINT wished number of DINT values to be stored in the array.
OK : DINT  return check.

Return values

  1. OK - array is allocated and ready for read / write operations.
  2. The specified ID is invalid or already used for another array.
  3. The specified size is invalid.
  4. Not enough memory (action denied by the Operating System).

The memory allocated by ARCREATE will be released when the application stops.

ARREAD: read array element

VAL := ARREAD (ID, POS);

ID : DINT  integer ID of the array.
POS : DINT index of the element in the array (first valid index is 0).
VAL : DINT value of the specified item or 0 if arguments are invalid.

ARWRITE: write array element

OK := ARWRITE (ID, POS, IN);

ID : DINT  integer ID of the array.
POS : DINT index of the element in the array (first valid index is 0).
IN : DINT  value to be assigned to the element.
OK : DINT  return check.

Return values

  1. OK - element was forced successfully
  2. The specified ID is invalid (not an allocated array).
  3. The specified index is invalid (out of array bounds).

Dynamic memory allocation functions

IEC 61131-3 Automation platform > Programming - Reference guide > Advanced operations > Dynamic memory allocation functions

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