DEFER INTERRUPT and the INT_FLAG

If the user selects Cancel during the CONSTRUCT, the built-in global integer variable INT_FLAG is automatically set to TRUE.

Once INT_FLAG is set to TRUE, your program must reset it to FALSE to detect a new cancellation. You typically set INT_FLAG to FALSE before you start a dialog instruction, and you test it just after (or in the AFTER CONSTRUCT / AFTER INPUT block) to detect if the dialog was canceled:

LET INT_FLAG = FALSE
CONSTRUCT BY NAME where_part
  ...
END CONSTRUCT
IF INT_FLAG = TRUE THEN
  ...
END IF

The statement DEFER INTERRUPT in your MAIN program block will prevent your program from terminating abruptly if a SIGINT signal is received. When using a GUI interface, the user can generate an interrupt signal if you have an action view named 'interrupt' (the predefined interrupt action). If an interrupt event is received, TRUE is assigned to INT_FLAG.

It is up to the programmer to manage the interruption event (stop or continue with the program), by testing the value of INT_FLAG variable.

Interruption handling is discussed in the report example, in Tutorial Chapter 9: Reports.