VAXTPU ERROR_HANDLERS — VMS 5.2

 Error Handlers

 An error handler is a block of code containing statements to be executed
 if VAXTPU generates a warning or an error.  Error handlers are optional
 and may be used either in procedures or in programs.  When used in
 programs (outside procedures) they must be placed after all the global
 declarations of constants, variables and procedures, and before any
 executable statements.  Only one error handler can be used in each
 procedure, and only one one can be used per program (outside procedures).

 VAXTPU error handlers are not usually recursive; that is, they do not
 apply their own statements to errors that arise while the error handler
 itself is being executed.  However, CTRL/C routines are an exception; they
 ARE recursive.

 Types of Error Handlers in VAXTPU

 VAXTPU has two types of error handlers:  procedure-style and case-style.

 The following example shows the syntax of a procedure-style error handler:

    ON_ERROR
      MESSAGE (ERROR_TEXT);
      MESSAGE ("Error on line " + STR (ERROR_LINE));
      RETURN;
    ENDON_ERROR

 The following example shows the syntax of a case-style error handler:

    ON_ERROR
        [TPU$_CONTROLC]:
       MESSAGE (ERROR_TEXT);
       RETURN (LEARN_ABORT);
        [OTHERWISE]:
       MESSAGE( ERROR_TEXT);
       RETURN;
    ENDON_ERROR

 Case-style error handlers are similar to VAXTPU case statements.  The
 statements in the handler have the general format:

    [error-keyword1,...error-keywordn] :  statement1;...statementn;

 The the selectors on the left-hand side of the colon in each statement
 must be either of the following:

 o  VAXTPU keywords indentifying errors or warnings

 o  The keyword OTHERWISE


 Case-style error handlers allow you to do the following:

 o  Trap the TPU$_CONTROLC status

 o  Specify an [OTHERWISE] selector specifying how to handle all errors and
    warnings that are not covered by specific selectors in the error
    handler.

 o  Suppress display of error and warning messages


 For more information on using error handlers, please refer to Chapter 3 of
 the VAXTPU Text Processing Utility Manual.

 Related Topics

    CALL_USER   ERROR   ERROR_LINE   ERROR_TEXT     LEARN_ABORT

    MESSAGE    MESSAGE_FLAGS       MESSAGE_TEXT   RETURN
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VAXTPU ERROR_HANDLERS — VMS 5.2
