Ubuntu Manpage: Error_handling - A set of routines for error handling in NCAR Graphics.

NAME

       Error_handling - A set of routines for error handling in NCAR Graphics.

SYNOPSIS

       ENTSR - Enters recovery mode.
       EPRIN - Prints the current error message.
       ERROF - Turns off the internal error flag.
       FDUM - A dump routine - the default version just RETURNS.
       ICFELL - Checks for an outstanding error condition.
       ICLOEM - Computes the real length of its character-string argument (ignoring blanks on the end)
       NERRO - Gets the current value of the internal error flag.
       RETSR - Restores a previous value of the internal error flag.
       SEMESS - Gets a specified portion of the current error message.
       SETER - Called by NCAR Graphics routines to report error conditions.

C-BINDING SYNOPSIS

       #include <ncarg/ncargC.h>

       c_entsr
       c_eprin
       c_errof
       c_icfell
       c_icloem
       c_nerro
       c_retsr
       c_semess
       c_seter

USING SETER IN NCAR GRAPHICS

There are specific conventions for the use of SETER within NCAR Graphics, as follows:

- All detectable errors shall be recoverable, in the sense described above. (That is, in every call to
SETER, the final argument shall be a 1, rather than a 2.) This is by request of the folks doing NCAR
Interactive, who rightly consider STOPs in the utilities undesirable. The idea is to let the user
decide what is to be done about the various error conditions.

- Whenever an NCAR Graphics routine calls a lower-level routine that might detect an error and call
SETER, it should subsequently use ICFELL to check the error state; if a recoverable error has
occurred, it should first do required clean-up chores, if possible, and then pass control back to the
routine that called it. In all such uses of ICFELL, the first argument should be the name of the
routine referencing ICFELL and the second argument should be a new number for the error, reflecting
the position of the reference to the lower-level routine in the upper-level routine.

- Any NCAR Graphics routine that can be called by a user and that can potentially yield a call to SETER
must immediately check the error state and, if that error state is non-zero, return control without
doing anything else. This is most conveniently done using a reference to ICFELL; see the second
example in the "Usage" section of the description of ICFELL. All such references should have a first
argument of the form 'XXXXXX - UNCLEARED PRIOR ERROR', where "XXXXXX" is the name of the routine in
which the reference occurs, and a second argument equal to "1".

- It is recommended that, within a given utility routine, the error numbers in references to SETER and
ICFELL should start at 1 and increment by 1. These numbers generally have no intrinsic meaning in
and of themselves: they are merely intended to allow a consultant to find the reference that
generated a given error.

- NCAR Graphics routines are not required to turn recovery mode on before calling a lower-level routine
that might call SETER (which was the convention in the PORT library, as described in the PORT
document). Instead, the assumption is that it is the responsibility of the user of NCAR Graphics to
set recovery mode if he/she desires to do recovery. Since, by default, recovery mode is turned off,
all NCAR Graphics calls to SETER will be treated as fatal: the error message will be printed and
execution will be terminated. Once the user turns recovery mode on, however, no NCAR Graphics error
will be treated in this way except for one that the user fails to recover from.

Note: These conventions are being adopted as of December 2, 1993, and represent a goal for the future.
The current situation is somewhat muddled: In some utilities, all SETER calls are fatal ones. In other
utilities, some SETER calls are fatal and some are not. In other utilities, no SETER calls are fatal. In
general, errors at a lower level are not detected and passed back up the call chain. Users have
complained (and rightly so) that error recovery is, in general, not possible; observance of these
conventions should help to fix the situation.

Further note: As of March 30, 1994, the situation has improved markedly. CONPACK and all utilities
referenced by it have been updated to follow the guidelines given above and work is proceeding on other
utilities.

There is one sticky area in which questions remains to be answered: Sometimes, when an error condition
occurs during execution of a utility routine that has changed the internal state of GKS or SPPS, it has
not been possible to restore the state of those packages to exactly what it was before that routine was
entered. In some cases, better bookkeeping would allow restoration to be done; in other cases, though,
restoration would involve calling a routine that could generate a call to SETER, which would cause a
STOP. In the latter cases, I have not yet worked out a good solution. For the moment, therefore, the
situation is this: if you call an NCAR Graphics utility with recovery mode turned on and, when you get
control back, you find that an error has occurred, you must be prepared to deal with the possibility that
at least the following things might been changed: 1) the current SET call; 2) the current polyline color
index; 3) the current polymarker color index; 4) the current text color index; 5) the current fill area
color index; 6) the current dash pattern.

ACCESS

       To use the Error_handling C or Fortran routines, load the NCAR Graphics libraries ncarg, ncarg_gks, and
       ncarg_c, preferably in that order.

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