Procedure

   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. 
 
   2) If the DAF to be searched has actually been closed, the error 
      will be diagnosed by routines called by 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 SPICEFALSE on output. 
 

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 (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

 
   1) See Particulars. 

Restrictions

 
   None. 
 

Literature_References

 
   NAIF Document 167.0, "Double Precision Array Files (DAF) 
   Specification and User's Guide" 
 

Author_and_Institution

 
   N.J. Bachman    (JPL) 
   W.L. Taber      (JPL) 
   I.M. Underwood  (JPL) 
 

Version

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

Index_Entries

 
   find previous daf array 
 

Link to routine daffpa_c source file daffpa_c.c