1Error_handling(3NCARG)           NCAR GRAPHICS          Error_handling(3NCARG)
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NAME

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

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

22       #include <ncarg/ncargC.h>
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24       c_entsr
25       c_eprin
26       c_errof
27       c_icfell
28       c_icloem
29       c_nerro
30       c_retsr
31       c_semess
32       c_seter
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USING SETER IN NCAR GRAPHICS

36       There are specific conventions for the use of SETER within NCAR
37       Graphics, as follows:
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39        -  All detectable errors shall be recoverable, in the sense described
40           above.  (That is, in every call to SETER, the final argument shall
41           be a 1, rather than a 2.) This is by request of the folks doing
42           NCAR Interactive, who rightly consider STOPs in the utilities
43           undesirable. The idea is to let the user decide what is to be done
44           about the various error conditions.
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46        -  Whenever an NCAR Graphics routine calls a lower-level routine that
47           might detect an error and call SETER, it should subsequently use
48           ICFELL to check the error state; if a recoverable error has
49           occurred, it should first do required clean-up chores, if possible,
50           and then pass control back to the routine that called it. In all
51           such uses of ICFELL, the first argument should be the name of the
52           routine referencing ICFELL and the second argument should be a new
53           number for the error, reflecting the position of the reference to
54           the lower-level routine in the upper-level routine.
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56        -  Any NCAR Graphics routine that can be called by a user and that can
57           potentially yield a call to SETER must immediately check the error
58           state and, if that error state is non-zero, return control without
59           doing anything else. This is most conveniently done using a
60           reference to ICFELL; see the second example in the "Usage" section
61           of the description of ICFELL. All such references should have a
62           first argument of the form 'XXXXXX - UNCLEARED PRIOR ERROR', where
63           "XXXXXX" is the name of the routine in which the reference occurs,
64           and a second argument equal to "1".
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66        -  It is recommended that, within a given utility routine, the error
67           numbers in references to SETER and ICFELL should start at 1 and
68           increment by 1.  These numbers generally have no intrinsic meaning
69           in and of themselves: they are merely intended to allow a
70           consultant to find the reference that generated a given error.
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72        -  NCAR Graphics routines are not required to turn recovery mode on
73           before calling a lower-level routine that might call SETER (which
74           was the convention in the PORT library, as described in the PORT
75           document).  Instead, the assumption is that it is the
76           responsibility of the user of NCAR Graphics to set recovery mode if
77           he/she desires to do recovery. Since, by default, recovery mode is
78           turned off, all NCAR Graphics calls to SETER will be treated as
79           fatal: the error message will be printed and execution will be
80           terminated. Once the user turns recovery mode on, however, no NCAR
81           Graphics error will be treated in this way except for one that the
82           user fails to recover from.
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84       Note: These conventions are being adopted as of December 2, 1993, and
85       represent a goal for the future. The current situation is somewhat
86       muddled: In some utilities, all SETER calls are fatal ones. In other
87       utilities, some SETER calls are fatal and some are not. In other
88       utilities, no SETER calls are fatal. In general, errors at a lower
89       level are not detected and passed back up the call chain. Users have
90       complained (and rightly so) that error recovery is, in general, not
91       possible; observance of these conventions should help to fix the
92       situation.
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94       Further note: As of March 30, 1994, the situation has improved
95       markedly.  CONPACK and all utilities referenced by it have been updated
96       to follow the guidelines given above and work is proceeding on other
97       utilities.
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99       There is one sticky area in which questions remains to be answered:
100       Sometimes, when an error condition occurs during execution of a utility
101       routine that has changed the internal state of GKS or SPPS, it has not
102       been possible to restore the state of those packages to exactly what it
103       was before that routine was entered. In some cases, better bookkeeping
104       would allow restoration to be done; in other cases, though, restoration
105       would involve calling a routine that could generate a call to SETER,
106       which would cause a STOP. In the latter cases, I have not yet worked
107       out a good solution. For the moment, therefore, the situation is this:
108       if you call an NCAR Graphics utility with recovery mode turned on and,
109       when you get control back, you find that an error has occurred, you
110       must be prepared to deal with the possibility that at least the
111       following things might been changed: 1) the current SET call; 2) the
112       current polyline color index; 3) the current polymarker color index; 4)
113       the current text color index; 5) the current fill area color index; 6)
114       the current dash pattern.
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ACCESS

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

122       Online: entsr, eprin, errof, fdum, icfell, icloem, nerro, retsr,
123       semess, seter, ncarg_cbind
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126       Copyright (C) 1987-2009
127       University Corporation for Atmospheric Research
128       The use of this Software is governed by a License Agreement.
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132UNIX                              March 1994            Error_handling(3NCARG)
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