Error Trapping

Error traps let you intercept and deal with run-time errors, rather than having programs unceremoniously abort or ignore a fatal error, possibly causing loss of data.

There are three steps you must take to trap errors, as described in the following sections:

Set the error trap. Use the ON ERROR GOTO statement.
Write the error-handling routine. The error-handling routine receives control when an error occurs.
Exit the error-handling routine. You exit the error handler using the RESUME statement so execution can continue at an appropriate location in the code.

For example, here is a piece of code that fills an array with the filenames from a directory. This section will add complete Error Trapping to prevent run-time errors when the user chooses a directory that does not have any files or a drive that is not ready.

SUB GetFileNames(File() AS STRING)

DIM CurrentDir AS STRING

DIM fName AS STRING, Mask AS STRING

DIM X AS INTEGER

Mask = "*.*"

CurrentDir = CURDIR$

Path = AskUserForPath$()

fName = DIR$(RTRIM$(Path) + Mask)

IF LEN(fName) = 0 THEN EXIT SUB

X = 1

WHILE LEN(fName)

Files(X) = fName

fName = DIR$

INCR X

WEND

END SUB