====== Error Handling ======

===== Defining an error handling routine =====

Starting from XC=BASIC version 3, certain runtime errors are trappable using the ''ON ERROR GOTO'' statement. You can specify a custom error handling routine that makes it possible to recover from errors when needed. The following example demonstrates this functionality:

<code xcbasic>
ON ERROR GOTO errhandler
DIM d$ AS STRING * 6

start:
  INPUT "enter divisor "; d$
  PRINT "10/"; d$; "="; 10.0 / VAL(d$)
  END

errhandler:
  IF ERR() = 20 THEN
    PRINT "division by zero error"
    GOTO start
  END IF
</code>

===== Getting the error code =====

When an error occurs, the ''ERR()'' function returns the error code, a number between 0 and 255. The following are built-in errors in XC=BASIC:

^ Code      ^ Error message       ^
|1              |TOO MANY FILES   |
|2              |FILE OPEN              |
|3              |FILE NOT OPEN      |
|4              |FILE NOT FOUND   |
|5              |DEVICE NOT PRESENT |
|6              |NOT INPUT FILE      |
|7              |NOT OUTPUT FILE  |
|8              |MISSING FILENAME|
|9              |ILLEGAL DEVICE NUMBER |
|10            |DEVICE NOT READY |
|11            |OTHER READ ERROR |
|14            |ILLEGAL QUANTITY |
|15            |OVERFLOW |
|20            |DIVISION BY ZERO |
|21            |ILLEGAL DIRECT |

===== User-defined errors =====

Apart from the built-in errors, you can define your own error codes, too. You can use the ''ERROR'' command to trigger any error, built-in or custom.

<code xcbasic>
ON ERROR GOTO errhandler
ERROR 99
END
errhandler:
  IF ERR() = 99 THEN PRINT "my custom error occured" ELSE PRINT "other error"
</code>