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Page 141S
SYSTEMS FUNCTIONS AND PROCEDURES
exception of a ControHC followed by a command to resume, Thus the
ERRORTRAP procedures themseLves have aborted to AMOS in most circtsnstances,
In addition STDERRORTRAP resets INFOP',XEOERR to zero before returning if
execution is to be resumed, This is because errors MUST NOT occur in the
error handler itseLf for obvious reasons,
AiphaPascal assumes it is
executing an error handler whenever XEQERR is nonzero, If an error does
occur within an error handier, the message
?Attempt to calL ERRORTRAP while in ERRORTRAP
is displayed, a direct abort to AMOS is made without closing any open files.
Thus, by reseting XEQERR to zero, STDERRORTRAP signals to
AlphaPascal
error handling is finished and further errors are again acceptable,
Should
you
that
decide not to call STDERRORTRAP at all, please keep in mind the
following points:
1,
The only errors from which you may safely resume execution are S (a
ControHC) and 10 (I/O error), An attempt to resume execution by
returning from ERRORTRAP with any other errors will probably crash
the system,
2,
It is acceptable to use EXIT to abort some function or procedure,
or 7our program, when any error occurs, Of course you can only
EXIT to leave a function or procedure which is currently active, so
you will probably want to have around some BOOLEAN variables to
keep track of whether or not you are currently within routines
which you might wish to EXIT from ERRORTRAP,
3.
Remember to set XEOERR
otherwise your next
back
error
to
will
zero
before leaving ERRORTRAP,
to AMOS without calling
abort
ER RO PT P A P
14,10,3
XERRORTRAP
When STDERRORTRAP is called by entering a Control"C, it is possible to
request a backtrace of suspended functions and procedures This backtrace
begins with the caller of the caller of STDERRORTRAP, which is usually the
caller of ERRORTRAP, and hence the routine which was suspended Thus,
should STDERRORTRAP be called by a function or procedure local to your
ERRORTRAP
procedure, the backtrace will begin in the wrong place,
he corrected by using XERRORTRAP, which takes a copy of the
as its argument,
It is used as follows:
(changed 30 April 1981)
system
This can
INFOPEC