Seter - A Centralized Error-Handling Package For Ncar Graphics
David J. Kennison
NCAR, P.O. Box 3000, Boulder, Colorado 80307-3000
Table of Contents
The routines described in this document are used for error-handling by NCAR
Graphics utilities. They are slightly modified versions of routines from
the PORT library. The basic error-handling routine is as follows:
- SETER - when an NCAR Graphics utility detects an error,
it calls this routine with three arguments: an error message, an error
number, and a flag indicating whether the error is "fatal" or
"recoverable". The following actions are taken:
The following routines are used to enter and/or leave recovery mode:
- If the error is fatal, SETER prints the error message, calls a
dump routine, and terminates execution of the user's program. (The
default dump routine does nothing; a user-written version may be
supplied to do something more useful.)
- If the error is recoverable, and if the user has not
put SETER into recovery mode, a recoverable error is handled in the same
way as a fatal one, but the dump routine is not called. If the user
has put SETER into recovery mode, SETER sets an internal
error flag equal to the error number, saves the error message, and
returns control to the user. In this case, the user is expected to test
for the occurrence of the recoverable-error condition, take suitable
remedial action, and turn off SETER's internal error flag; if the user
does not do this, then, on the next call to SETER, both
error messages (the remembered one and the one from that next call to
SETER) are printed and execution is terminated.
The following routines are of use during recovery from an error:
- ENTSR is normally called to enter recovery mode. The
internal recovery-mode flag is given a new value; the previous value of
the flag is returned to the caller.
- RETSR is normally called to leave recovery mode; it
just resets the internal recovery-mode flag to a user-specified value,
normally one returned by an earlier call to ENTSR.
The following routine exists only to be replaced by the user:
- EPRIN, when called, prints the error message associated
with the internal error flag, if that flag is non-zero. If the internal
error flag is zero, EPRIN does nothing.
- NERRO is a function whose value is that of the internal
error flag of SETER. The value will be non-zero if and only if a
recoverable error has occurred and the flag has not yet been cleared by
- SEMESS is a function of type CHARACTER whose value is
either a requested portion of the error message for the error that
caused the internal error flag to be set non-zero, if that flag
is non-zero, or just blanks, otherwise.
- ICLOEM is a function whose value is the "actual" length
of the error message defined by its single (character-string) argument
(ignoring blanks on the right end of the string).
- ERROF turns off the internal error flag of SETER and
should be called only after remedial action has been taken to recover
from an error.
The following routine is provided for use in any routine that calls another
routine which can, directly or indirectly, call SETER:
- FDUM is the dump routine that is called by SETER when
it is handling a fatal error. The default version of this routine just
RETURNs; a user-written version may be supplied to do something more
- ICFELL is a function of type INTEGER whose value is
that of the internal error flag at the time ICFELL is entered. There
are two arguments; when the value of ICFELL is non-zero, these arguments
specify how the current internal error flag and error message are to be
This section contains detailed descriptions of all the error-handling
The FORTRAN statement "CALL SETER (MESSG,NERRF,ILEVL) is used to tell
the error-handling package that an error has occurred. Exactly what
happens as a result of such a call depends not only on the values of
the arguments, but on the settings of two internal variables: the error
flag, which says whether or not there was a prior error, and the
recovery-mode flag, which says whether or not recovery mode is in
MESSG (an input variable or constant of type CHARACTER)
is an error message describing the error that has occurred. This should
be of the form "XXXXXX - TEXT DESCRIBING THE ERROR", where "XXXXXX" is
the name of the routine in which the error occurred, and it should not
be more than 113 characters long.
- If the internal error flag is 0 (no prior error) and the internal
recovery-mode flag is 2 (recovery mode not set, which is the default),
SETER prints the error message MESSG, calls FDUM if and only if ILEVL
= 2, and then STOPs.
- If the internal error flag is 0 (no prior error) and the internal
recovery-mode flag is 1 (recovery mode set), then what happens depends
on the value of ILEVL: If ILEVL = 1 (recoverable error), SETER resets
the internal error flag = NERRF, remembers the error message MESSG,
and RETURNs; the user is then expected to detect the fact that an
error has occurred, take the necessary remedial action, and call
ERROF to turn the internal error flag off. If ILEVL = 2 (fatal
error), SETER prints the error message MESSG, calls FDUM, and STOPs.
- If the internal error flag is non-zero (prior error), then the value
of the internal recovery-mode flag will be 1 (recovery mode set). In
this case, it doesn't make any difference what the value of ILEVL is:
SETER prints both the remembered error message from the prior error
and the new error message from MESSG, calls FDUM, and STOPs.
NERRF (an input expression of type INTEGER) is a
non-zero error number in the range from -999 to +9999.
ILEVL (an input expression of type INTEGER) is the
"error level" - either a 1 or a 2, implying that the error described
by MESSG and NERRF is recoverable or fatal, respectively.
The FORTRAN statement "CALL ENTSR (IROLD,IRNEW)" is normally used to
enter recovery mode and save the previous value of the internal
recovery-mode flag, but it can also be used to exit from recovery mode
and save the previous value of the flag, or to just get the value of
the flag, without changing it.
If recovery mode is turned off by a call to ENTSR at a time when the
internal error flag is non-zero, this is treated as a fatal error; the
error message is printed, the dump routine FDUM is called, and a STOP
IROLD (an output variable of type INTEGER) receives
the old value of the internal flag that indicates whether recovery mode
is in effect or not. In the former case, the returned value will be
a 1; in the latter case, it will be a 2. Normally, the value returned
is saved for a later call to RETSR.
IRNEW (an input expression of type INTEGER) specifies
what is to be done to the internal flag that indicates whether recovery
mode is in effect or not. If IRNEW is a 1 or a 2, it becomes the new
value of the internal recovery-mode flag: the value 1 turns recovery
mode on and the value 2 turns it off. Other non-zero values are illegal,
but, if IRNEW is zero, the state of the internal recovery-mode flag is
The FORTRAN statement "CALL RETSR (IROLD)" is normally used to return
the internal flag of SETER that says whether or not recovery mode is
in effect to the state that it was in before some past call to ENTSR.
If recovery mode is turned off by a call to RETSR at a time when the
internal error flag is non-zero, this is treated as a fatal error;
the error message is printed, the dump routine FDUM is called, and
a STOP is executed.
IROLD (an input expression of type INTEGER) specifies
a desired value for the internal flag that indicates whether recovery
mode is in effect or not. The value 1 turns recovery mode on and the
value 2 turns it off. Normally, one uses a value of IROLD that was
previously returned by a call to ENTSR.
If SETER's internal error flag is non-zero, the FORTRAN statement
"CALL EPRIN" prints the remembered error message associated with
the non-zero value. Otherwise, EPRIN does nothing.
The expression "NERRO(NERRF)" has the value of the internal error flag
of SETER. If its value is non-zero, this indicates that a prior
recoverable error occurred and has not yet been cleared. The argument
NERRF is given the same value as the function reference; this is useful
in some situations.
NERRF (an output variable of type INTEGER) receives
the same value that is returned as the value of the function itself.
If the internal error flag of SETER is non-zero, the value of the
character expression "SEMESS(ITRIM)" is the remembered error message
associated with that error flag, trimmed as indicated by the value of
the input quantity ITRIM. Otherwise, it is a string of blanks. In any
routine that references SEMESS, it must be declared to be of type
CHARACTER*113. Assume that the current error message is as follows:
'CPCLAM/AREDAM - AREA-MAP ARRAY OVERFLOW'
Then, one could use SEMESS as follows:
SEMESS(0)='CPCLAM/AREDAM - AREA-MAP ARRAY OVERFLOW'
SEMESS(1)='AREDAM - AREA-MAP ARRAY OVERFLOW'
SEMESS(2)='AREA-MAP ARRAY OVERFLOW'
When ITRIM = 0 or less, no trimming is done; the whole error message
is returned. When ITRIM = 1, prepended routine names and the associated
slashes are trimmed off. When ITRIM = 2 or greater, all leading routine
names are trimmed off; just the error description is returned.
ITRIM (an input expression of type INTEGER) says what
part of the error message is to be returned, as detailed above in the
section called "Usage".
The value of the expression "ICLOEM(MESSG)" is the actual length of
the non-blank portion of the input character variable MESSG. Thus,
"MESSG(1:ICLOEM(MESSG))" is the non-blank part of MESSG. (It is assumed
that the non-blank part of MESSG is left-justified in the character
string, with blank fill to the right, as is the case for all NCAR
Graphics error messages in calls to SETER.)
MESSG (an input variable or constant of type CHARACTER)
is most likely an error message returned by a reference to the function
The FORTRAN statement "CALL ERROF" turns off (zeroes) SETER's internal
This subroutine is not intended to be called by the user. It is called
by SETER when a fatal error is being processed and a STOP is about to
be executed. The default version of FDUM does nothing. A user-supplied
replacement version may take some other (system-dependent or
program-dependent) action which would be helpful in diagnosing what
may have caused the error to occur.
ICFELL (which stands for "I Check For Errors on Lower Level") is used
to check for the occurrence of a recoverable error in a lower-level
routine and (perhaps) to update the current internal error message and
The old value of the error flag is returned as the value of the function
ICFELL. If that value is zero, nothing else has been done. If the value
of ICFELL is non-zero, the following actions have been taken:
An example: Assume that the routine "A" calls the
routine "B" and that "B" detects an error and calls SETER with error
number "32" and error message 'B - ERROR HAS OCCURRED'. If recovery
mode is not in effect, SETER prints the error message
and STOPs; if recovery mode is in effect, control
returns from "SETER" to "B" and thence to "A". At that point, the
- If MESSG is blank, the current error message has not been changed.
- If MESSG is non-blank and its length is 6 or less, it should be the
name of the routine referencing ICFELL; the current error message
has been altered by prepending first a slash and then MESSG. (Note
that, if an error occurs several levels deep, the effect of using
ICFELL in this manner at each level is, effectively, to generate
traceback information in the error message.)
- If MESSG is non-blank and its length is 7 or greater, its value has
become the new value of the current error message and the previous
error message has been printed. This is intended for use at the
beginning of an NCAR Graphics routine to check for an outstanding
error that the user has not recovered from and to ensure that the
message for the outstanding error gets printed.
- If the expression NERRF has the value zero, the current error flag
has not been changed.
- If the expression NERRF has a non-zero value, the value of the
current error flag has been made equal to that value.
IF (ICFELL('A',13).NE.0) RETURN
detects the fact that an error has occurred in "B" and results in a
return from "A" to whatever routine called it. It also changes the
current error message to read 'A/B - ERROR HAS OCCURRED' and changes
the error number from "32" to "13".
Another example: Assume that the NCAR Graphics routine
"A" is called when recovery mode is set and that it detects an error,
calls SETER, and RETURNs to the user. If the user neglects to check the
error state and calls the routine "B" next, the statement
IF (ICFELL('B - UNCLEARED PRIOR ERROR',1).NE.0) RETURN
ensures that the error message from routine "A" will be printed, that
it will be replaced by an error message referring to the routine "B",
and that "B" won't do anything else.
MESSG (an input variable or constant of type CHARACTER)
is a character string saying what is to be done to the current error
message (when an error has occurred). If MESSG is blank, no change is
to be made in the current error message. If the length of MESSG is six
characters or fewer, a slash is prepended to the current error message
and then MESSG is prepended to that. If the length of MESSG is seven
characters or more, MESSG is a complete new error message to be
substituted for the current one.; it should be of the form "XXXXXX -
TEXT DESCRIBING THE ERROR", where "XXXXXX" is the name of the routine
in which the error occurred, and it should not be more than 113
NERRF (an input expression of type INTEGER) has a value
in the range from -999 to +9999. If this value is zero, no change is made
in the internal error flag; otherwise, it is the desired new value of
that flag (when an error has occurred).
There are specific conventions for the use of SETER within NCAR Graphics,
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.
- 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 consider STOPs in the utilities undesirable. The idea
is to let the user decide what is to be done about the various error
- 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
- 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.
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
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 one or more of 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.
The NCAR Graphics examples named "tseter" and "arex02" illustrate the
use of SETER and associated routines; the former demonstrates minimal
functioning of SETER and the latter demonstrates how to use the
package in a real situation: to recover from area-map array overflow
errors in the package AREAS.
Note: An example named "xxxxxx"may be obtained, on a Unix
system on which NCAR Graphics is installed, by typing the command "ncargex
xxxxxx". A file called "xxxxxx.f" will be copied into the current working
directory, compiled, and executed. If a metafile is produced, it will have
the name "xxxxxx.ncgm". The command "ncargex -n xxxxxx" may be used to get
the source file "xxxxxx.f" without compiling or executing it.