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Technical Information

Application Development Manual | Processing run-time errors (error trapping)

Processing run-time errors (error trapping)

Function

Use error trapping to process run-time errors in programs.

Syntax

Detailed Description

Run-time errors frequently accompany communications and other operations even during normal use, so such user application programs should use error trapping to provide their own built-in recovery processing.

The ON ERROR GOTO statement specifies a label giving the starting point for this processing whenever there is a run-time error. Alternatively, specifying 0 disables error trapping.

Returnlocation specifies how the recovery processing returns the program to normal processing. (See Table.)

Setting	Return target after error processing
Blank	Statement triggering run-time error
0	Statement triggering run-time error
NEXT	Statement following one triggering run-time error
Other label	Line specified by the label

The ERR and ERL functions provide additional information about the run-time error and its location. The error processing routine can branch on the error type, for example.

Example

Retry if a file transfer encounters an error

  private tempkey$         ' declare variable
open "COM1:115200" as #1 ' open communications device file
out &h6060, 3
on error goto ERRCOM     ' branch to ERRCOM on communications errors
xfile "TEST1.DAT"        ' Send file
on error goto 0
close #1
end
ERRCOM:
print "Transmission error!"
print "CODE:";hex$(ERR);
print " ADDR:";hex$(ERL)
print "Press a key to retry.";
tempkey$ = input$(1)
resume 0