Handling type conversion errors

Runtime errors can be handled on type conversion failures.

By default, in cases of type conversion or overflow errors, the program continues, the target variable is set to NULL and the global status variable is not set.

In order to detect data conversion and overflow errors, use the WHENEVER ANY ERROR statement.

This code example shows use of the WHENEVER ANY ERROR statement:

MAIN  -- DBDATE set to Y4MD-
  DEFINE v VARCHAR(50), d DATE
  LET v = "2012-99-99"      -- invalid date string
  LET d = v
  DISPLAY status, "/", NVL(d,"NULL")  -- displays 0/NULL
  WHENEVER ANY ERROR CONTINUE
  LET d = v
  DISPLAY status, "/", NVL(d,"NULL")  -- displays -1205/NULL
  WHENEVER ANY ERROR STOP
  LET d = "2012-11-23"  -- valid date, ok
  DISPLAY status, "/", NVL(d,"NULL")  -- displays 0/2012-11-23
  LET d = v   -- program execution stopped with error -1205
END MAIN

The code above will produce the following output:

          0/NULL
      -1218/NULL
Program stopped at 'x.4gl', line number 10.
FORMS statement error number -1218.
String to date conversion error.

Conversion and overflow errors are implicitly trapped in TRY/CATCH blocks.

In this example, the INTERVAL variable is not large enough to hold the result of d2 - d1:

MAIN
  DEFINE d1, d2 DATETIME YEAR TO FRACTION(5)
  DEFINE i INTERVAL SECOND(2) TO SECOND
  LET d1 = "2015-11-06 17:40:21.436"
  LET d2 = "2015-11-06 10:40:21.436"
  TRY
      LET i = d2 - d1
  CATCH
      DISPLAY status, " / ", err_get(status)
  END TRY
END MAIN

Above code will produce the following output:

      -1265 / Overflow occurred on a datetime or interval operation.