Attribute ‘no_assign’

This pragma causes compiler errors to be displayed if an instance of the function block is assigned to another instance of the same function block. Such assignments are often to be avoided if the function block contains pointers and pointers lead to problems, because they are copied as well during the value assignment.

Syntax:

{attribute 'no_assign'}

Insertion position: first line in the declaration part of a function block.

Example

Assignment of function block instances containing pointers.

In this example the value assignment of the function block instances will lead to problems during the execution of fb_exit:

VAR_GLOBAL
 inst1 : TestFB;
 awsBufferLogFile : ARRAY [0..9] OF WSTRING(66);(* Area: 0, Offset: 0x1304 (4868)*)
 LogFile : SEDL.LogRecord := (sFileName := 'LogFile.log', pBuffer := ADR(awsBufferLogFile), udiMaxEntriesFile := UDINT#10000, udiMaxBuffered := UDINT#10, uiLineSize := UINT#64, wsSep := " ", xCircular := TRUE, siDateFormat := SINT#0, siTimeFormat := SINT#0);
END_VAR

PROGRAM PLC_PRG
VAR
 inst2 : TestFB := inst1;
 LogFileNew
END_VAR

In this case LogRecord manages a list of pointers, for which various actions are executed in the case of fb_exit. Problems result due to the assignment, because fb_exit will be executed twice. You should prevent this by adding the attribute 'no_assign' in the declaration of the function block TestFB:

{attribute 'no_assign'}
FUNCTION_BLOCK TestFB
VAR_INPUT
...

The following compile errors are then displayed:

C0328: Assignment not allowed for type TestFB
C0328: Assignment not allowed for type LogRecord