Procedure

   daffpa_c ( DAF, find previous array ) 

   void daffpa_c ( SpiceBoolean  * found )

Abstract

   Find the previous (backward) array in the current DAF.

Required_Reading

   DAF

Keywords

   FILES

Brief_I/O

   VARIABLE  I/O  DESCRIPTION
   --------  ---  --------------------------------------------------
   found      O   SPICETRUE if an array was found.

Detailed_Input

   None.

Detailed_Output

   found       is SPICETRUE if an array was found, and is SPICEFALSE
               if, when this routine is called, the current array is
               the head of the array list. (Recall that the arrays in
               a DAF may be viewed as a doubly linked list, with the
               head being the first array in the file.)

Parameters

   None.

Exceptions

   1)  If this routine is called before a search is begun, the error
       SPICE(DAFNOSEARCH) is signaled by a routine in the call tree of this
       routine.

   2)  If the DAF to be searched has actually been closed, an error
       is signaled by a routine in the call tree of this routine.

   3)  If the beginning of the array list has already been reached
       when this routine is called, this routine will not change the
       current array. `found' will be false on output.

   4)  If the summary record of the next (backward) record in the DAF
       file cannot be read, the error SPICE(RECORDNOTFOUND) is
       signaled by a routine in the call tree of this routine.

Files

   None.

Particulars

   The DAF search routines are:


      dafbfs_c       Begin forward search.
      daffna         Find next array.

      dafbbs_c       Begin backward search.
      daffpa_c       Find previous array.

      dafgs_c        Get summary.
      dafgn_c        Get name.
      dafgh_c        Get handle.

      dafcs_c        Continue search.

   The main function of these entry points is to allow the
   contents of any DAF to be examined on an array-by-array
   basis.

   Conceptually, the arrays in a DAF form a doubly linked list,
   which can be searched in either of two directions: forward or
   backward. It is possible to search multiple DAFs simultaneously.

   dafbfs_c (begin forward search) and daffna are used to search the
   arrays in a DAF in forward order. In applications that search a
   single DAF at a time, the normal usage is

      dafbfs_c ( handle );
      daffna_c ( &found );

      while ( found )
      {
         dafgs_c ( sum  );
         dafgn_c ( name );
          .
          .

         daffna_c ( &found );
      }


   dafbbs_c (begin backward search) and daffpa_c are used to search the
   arrays in a DAF in backward order. In applications that search
   a single DAF at a time, the normal usage is

      dafbbs_c ( handle );
      daffpa_c ( &found );

      while ( found )
      {
         dafgs_c ( sum  );
         dafgn_c ( name );
          .
          .

         daffpa_c ( &found );
      }


   In applications that conduct multiple searches simultaneously,
   the above usage must be modified to specify the handle of the
   file to operate on, in any case where the file may not be the
   last one specified by dafbfs_c or dafbbs_c. The routine dafcs_c
   (DAF, continue search) is used for this purpose. Below, we
   give an example of an interleaved search of two files specified
   by the handles handl1 and handl2. The directions of searches
   in different DAFs are independent; here we conduct a forward
   search on one file and a backward search on the other.
   Throughout, we use dafcs to specify which file to operate on,
   before calling daffna_c, daffpa_c, dafgs_c, or dafgn_c.


      dafbfs_c ( handl1 );
      dafbbs_c ( handl2 );

      dafcs_c  ( handl1  );
      daffna_c ( &found1 );

      dafcs_c  ( handl2  );
      daffpa_c ( &found2 );

      while ( found1 || found2 )
      {
         if ( found1 )
         {
            dafcs_c ( handl1 );
            dafgs_c ( sum    );
            dafgn_c ( name   );
             .
             .
            dafcs_c  ( handl1  );
            daffna_c ( &found1 );
         }

         if ( found2 )
         {
            dafcs_c ( handl2 );
            dafgs_c ( sum    );
            dafgn_c ( name   );
             .
             .
            dafcs_c  ( handl2  );
            daffpa_c ( &found2 );
         }
      }


   At any time, the latest array found (whether by daffna_c or daffpa_c)
   is regarded as the "current" array for the file in which the
   array was found. The last DAF in which a search was started,
   executed, or continued by any of dafbfs_c, dafbbs_c, daffna_c,
   daffpa_c or dafcs_c is regarded as the "current" DAF. The summary
   and name for the current array in the current DAF can be obtained
   separately, as shown above, by calls to dafgs_c (get summary) and
   dafgn_c (get name). The handle of the current DAF can also be
   obtained by calling dafgh_c (get handle).

   Once a search has been begun, it may be continued in either
   direction. That is, daffpa_c may be used to back up during a
   forward search, and daffna_c may be used to advance during a
   backward search.

Examples

   The numerical results shown for these examples may differ across
   platforms. The results depend on the SPICE kernels used as input,
   the compiler and supporting libraries, and the machine specific
   arithmetic implementation.

   1) See -Particulars.

   2) Create a simple program to output the double precision and integer
      values stored in an SPK's segments' descriptors. This function
      opens a DAF for read, performs a backwards search for the DAF
      arrays, prints the segment descriptor for each array found, then
      closes the DAF.

      Use the SPK kernel below as input DAF file for the program.

         de421.bsp


      Example code begins here.


      /.
         Program daffpa_ex1
      ./
      #include <stdio.h>
      #include "SpiceUsr.h"

      int main()
         {

         /.
         Local constants
         ./

         /.
         Define the summary parameters appropriate
         for an SPK file.
         ./

         #define ND              2
         #define NI              6
         #define MAXSUM          125

         SpiceInt                ic  [ NI ];
         SpiceInt                handle;

         SpiceDouble             dc  [ ND ];
         SpiceDouble             sum [ MAXSUM ];

         SpiceChar             * kernel = "de421.bsp";

         SpiceBoolean            found;


         /.
         Open a DAF for read. Return a handle referring to the file.
         ./
         dafopr_c ( kernel, &handle );

         /.
         Begin a backward search on the file.
         ./
         dafbbs_c ( handle );

         /.
         Search until a DAF array is found.
         ./
         daffpa_c ( &found );

         /.
         Loop while the search finds subsequent DAF arrays.
         ./
         while ( found )
            {

            dafgs_c ( sum );
            dafus_c ( sum, ND, NI, dc, ic );

            printf( " Doubles: %f %f \n", dc[0], dc[1] );
            printf( "Integers: %d %d %d %d %d %d\n\n",
                       (int)ic[0], (int)ic[1], (int)ic[2],
                       (int)ic[3], (int)ic[4], (int)ic[5] );

            /.
            Check for another segment.
            ./
            daffpa_c ( &found );
            }

         /.
         Safely close the DAF.
         ./
         dafcls_c ( handle  );

         return ( 0 );
         }


      When this program was executed on a Mac/Intel/cc/64-bit
      platform, the output was:


       Doubles: -3169195200.000000 1696852800.000000
      Integers: 499 4 1 2 2098633 2098644

       Doubles: -3169195200.000000 1696852800.000000
      Integers: 299 2 1 2 2098621 2098632

       Doubles: -3169195200.000000 1696852800.000000
      Integers: 199 1 1 2 2098609 2098620

       Doubles: -3169195200.000000 1696852800.000000
      Integers: 399 3 1 2 1521325 2098608

       Doubles: -3169195200.000000 1696852800.000000
      Integers: 301 3 1 2 944041 1521324

       Doubles: -3169195200.000000 1696852800.000000
      Integers: 10 0 1 2 820837 944040

       Doubles: -3169195200.000000 1696852800.000000
      Integers: 9 0 1 2 785633 820836

       Doubles: -3169195200.000000 1696852800.000000
      Integers: 8 0 1 2 750429 785632

       Doubles: -3169195200.000000 1696852800.000000
      Integers: 7 0 1 2 715225 750428

       Doubles: -3169195200.000000 1696852800.000000
      Integers: 6 0 1 2 674741 715224

       Doubles: -3169195200.000000 1696852800.000000
      Integers: 5 0 1 2 628977 674740

       Doubles: -3169195200.000000 1696852800.000000
      Integers: 4 0 1 2 567373 628976

       Doubles: -3169195200.000000 1696852800.000000
      Integers: 3 0 1 2 423049 567372

       Doubles: -3169195200.000000 1696852800.000000
      Integers: 2 0 1 2 310405 423048

       Doubles: -3169195200.000000 1696852800.000000
      Integers: 1 0 1 2 641 310404


      Note, the final entries in the integer arrays contain the segment
      start/end indexes. The output indicates the search proceeded
      from the end of the file (high value index) towards the beginning
      (low value index).

Restrictions

   None.

Literature_References

   None.

Author_and_Institution

   N.J. Bachman        (JPL)
   J. Diaz del Rio     (ODC Space)
   W.L. Taber          (JPL)
   I.M. Underwood      (JPL)
   E.D. Wright         (JPL)

Version

   -CSPICE Version 1.0.3, 25-AUG-2021 (JDR)

       Edited the header to comply with NAIF standard. Added
       entry #4 to -Exceptions section.

   -CSPICE Version 1.0.2, 28-JUN-2016 (EDW)

       Edit to Example code, SpiceInts output as ints using
       explicit casting.

   -CSPICE Version 1.0.1, 10-OCT-2012 (EDW)

       Added a functional code example to the -Examples section.

       Removed the obsolete Reference citation to "NAIF
       Document 167.0."

   -CSPICE Version 1.0.0, 31-JUL-1999 (NJB) (WLT) (IMU)

Index_Entries

   find previous DAF array