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Syntax
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On Error
{Goto label |
Resume Next
| Goto 0}
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Description
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Defines the action taken when a trappable runtime error occurs.
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Comments
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The form
O
n Error Goto
label causes execution to transfer to the specified label when a runtime error occurs.
The form
On Error Resume Next
causes execution to continue on the line following the line that caused the error.
The form
On Error Goto 0
causes any existing error trap to be removed.
If an error trap is in effect when the script ends, then an error will be generated.
An error trap is only active within the subroutine or function in which it appears.
Once an error trap has gained control, appropriate action should be taken, and then control should be resumed using the
Resume
statement. The
Resume
statement resets the error handler and continues execution. If a procedure ends while an error is pending, then an error will be generated. (The
Exit Sub
or E
xit Function
statement also resets the error handler, allowing a procedure to end without displaying an error message.)
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Errors within an Error Handler
If an error occurs within the error handler, then the error handler of the caller (or any procedure in the call stack) will be invoked. If there is no such error handler, then the error is fatal, causing the script to stop executing. The following statements reset the error state (that is, these statements turn off the fact that an error occurred):
Resume
Err=-1
The
Resume
statement forces execution to continue either on the same line or on the line following the line that generated the error. The
Err=-1
statement allows explicit resetting of the error state so that the script can continue normal execution without resuming at the statement that caused the error condition.
The
On Error
statement will not reset the error. Thus, if an
On Error
statement occurs within an error handler, it has the effect of changing the location of a new error handler for any new errors that may occur once the error has been reset.
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Example
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This example will demonstrate three types of error handling. The first case simply by-passes an expected error and continues with program operation. The second case creates an error branch that jumps to a common error handling routine that processes incoming errors, clears the error (with the Resume statement) and resumes program execution. The third case clears all internal error handling so that execution will stop when the next error is encountered.
Sub Main()
Dim x%
a = 10000
b = 10000
On Error Goto Pass 'Branch to this label on error.
Do
x% = a * b
Loop
Pass:
Err = -1 'Clear error status.
MsgBox "Cleared error status and continued."
On Error Goto Overflow 'Branch to new error routine on any
x% = 1000 'subsequent errors.
x% = a * b
x% = a / 0
On Error Resume Next 'Pass by any following errors until
x% = 1000 'another On Error statement is
x% = a * b 'encountered.
On Error Goto 0 'Clear error branching.
x% = a * b 'Program will stop here.
Exit Sub 'Exit before common error routine.
Overflow: 'Beginning of common error routine.
If Err = 6 then
MsgBox "Overflow Branch."
Else
MsgBox Error(Err)
End If
Resume Next
End Sub
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See Also
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Error Handling (topic); Error (statement); Resume (statement).
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CIMPLICITY