16.1 
Trapping and
handling errors
If execution of a macro causes an error in WordPerfect (e.g., if
the macro attempts to open a file that does not exist), or the
macro executes a search that returns a "not found," the macro
will end with the error or not-found message box displayed on the
screen. This looks ugly and can be disconcerting to the user, so
you might want to prevent it. Or you may want to have
the macro perform alternative operations, depending on whether a
not-found or error condition was encountered or not. To handle
these situations you can "trap" these conditions and have the
macro perform some
other action (rather than having the system display the usual
message boxes and terminate the macro).
16.2
The OnNotFound() and OnError() commands
The commands OnNotFound() and
OnError are used to have the macro perform
certain actions when a not-found or error condition is
encountered, respectively. Specifically, they instruct the macro
to jump to a label in the macro as soon as the not-found or error
condition is encountered, and resume execution at that point.
(This is similar to the operation of the Go()
command.) These error-trapping commands must be executed
before the command that would cause the not-found or
error condition to occur. For example, you would put the
OnNotFound command before the search command to
which it applies.
The form of these commands are:
OnNotFound([labelname])
OnError([labelname])
where the label name identifies the point in the macro that
you want to jump to when the condition occurs; that point is
marked with a Label() with that name.
An OnNotFound() command remains in effect in
a macro until another OnNotFound() command is
executed (with an instruction to jump to a different label). The
same is true for the OnError() command. If no
labelname is specified, error and not-found conditions will be
processed as they normally would be by WordPerfect, so the
commands OnNotFound() and
OnError() will "reset" the program behavior for
these conditions to the default.
One place where you might want to use the
OnNotFound() command is in a macro that performs
a search repeatedly throughout the document, performing the same
action each time it finds the search string (i.e., in a loop).
This is often necessary to make repeated identical changes that
cannot be accomplished by a global replace. Eventually the
search will fail because no further occurrences of the search
string exist, and normally the ugly "not found" box would be
displayed.
To avoid this, you can just put a label at the very end of the
macro, and
insert a OnNotFound() command to jump to that
label when the search fails. Since that Label()
is the last command in the macro, the macro simply ends, without
a "not found" box displayed. Of course, you need not end the
macro at that point; you could insert commands for the macro to
continue to do additional processing.
Another occasion to use error-trapping is when you want the
macro to perform two different operations, depending on whether
some text exists or not. The macro code for this would be:
|
OnNotFound(NotThere@)
SearchString([string to look
for])
SearchNext()
|
| |
[commands to be executed if text
exists] |
|
| |
|
| |
Label(NotThere@)
|
| |
[commands to be executed if text does not
exists] |
An alternative method of handling not-found conditions is to
use the NotFound() command, and/or the
?NotFound system variable. These commands are
beyond the scope of this tutorial.
