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The pages on this site contain documentation for very old MS-DOS software, purely for historical purposes. If you're looking for up-to-date documentation, particularly for programming, you should not rely on the information found here, as it will be woefully out of date.

  ◄Programming Tasks►   ◄Trapping►   ◄Contents►   ◄Index►
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Statements and Functions Used for Trapping Events and Errors
 
Task               Statement or Function                Action
 
Trapping errors    ON ERROR GOTO line       Causes a program to branch to
while a program                             the given line where line
is running                                  refers either to a line number
                                            or line label. Branching takes
                                            place whenever an error occurs
                                            during execution.
 
                   RESUME                   Returns control to the program
                                            after executing an error-handling
                                            routine. The program resumes at
                                            either the statement causing the
                                            error (RESUME [0]), the statement
                                            after the one causing the error
                                            (RESUME NEXT), or the line iden-
                                            tified by line (RESUME line).
 
Getting            ERR                      Returns the code for an error
error-status                                that occurs at run time
data
                   ERL                      Returns the number of the line
                                            on which an error occurred
                                            (useful only if program has
                                            line numbers)
 
                   ERDEV                    Returns a device-specific error
                                            code for the last device (such
                                            as a printer) for which DOS
                                            detected an error
 
                   ERDEV$                   Returns the name of the last
                                            device for which DOS detected
                                            an error
 
Defining your      ERROR                    Simulates the occurrence of
own error codes                             a BASIC error; can also be used
                                            to define an error not trapped
                                            by BASIC
 
Trapping events    ON event GOSUB line      Causes a branch to the
while a program                             subroutine starting with line,
is running                                  where line refers either to a
                                            line number or line label,
                                            whenever the given event occurs
                                            during execution.
 
                   event ON                 Enables trapping of the given
                                            event
 
                   event OFF                Disables trapping of the given
                                            event
 
                   event STOP               Suspends trapping of the given
                                            event
 
                   RETURN                   Returns control to the program
                                            after executing an event-handling
                                            subroutine. The program resumes
                                            at the statement immediately
                                            following the place in the
                                            program where the event occurred
                                            (RETURN), or the line that is
                                            identified by line (RETURN line).