GWBASIC User's Manual

GW-BASIC User's Guide
ON ERROR GOTO Statement
Purpose:
To enable error trapping and specify the first line of the error-handling subroutine.
Syntax:
ON ERROR GOTO line number
Comments:
Once error trapping has been enabled, all errors detected by GW-BASIC, including direct mode
errors, (for example, syntax errors) cause GW-BASIC to branch to the line in the program which
begins the specified error-handling subroutine.
GW-BASIC branches to the line specified by the ON ERROR statement until a RESUME statement
is found.
If line number does not exist, an "Undefined line" error results.
To disable error trapping, execute the following statement:
ON ERROR GOTO 0
Subsequent errors print an error message and halt execution.
An ON ERROR GOTO 0 statement in an error-trapping subroutine causes GW-BASIC to stop and
print the error message for the error that caused the trap. It is recommended that all error-trapping
subroutines execute an ON ERROR GOTO 0 if an error is encountered for which there is no
recovery action.
If an error occurs during execution of an error-handling subroutine, the GW-BASIC error
message is printed and execution terminated. Error trapping does not occur within the errorhandling
subroutine.
Examples:
10 ON ERROR GOTO 1000
.
.
.
1000 A=ERR: B=ERL
1010 PRINT A, B
1020 RESUME NEXT
Line 1010 prints the type and location of the error on the screen (see the ERR and ERL variables).
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