Procedure

   diff_c ( Difference of two sets ) 

   void diff_c (  SpiceCell   * a,
                  SpiceCell   * b,
                  SpiceCell   * c  )

Abstract

   Take the difference of two sets of any data type to form a third
   set.

Required_Reading

   SETS

Keywords

   CELLS
   SETS

Brief_I/O

   VARIABLE  I/O  DESCRIPTION
   --------  ---  --------------------------------------------------
   a          I   First input set.
   b          I   Second input set.
   c          O   Difference of `a' and `b'.

Detailed_Input

   a           is a SPICE set.

               `a' must be declared as a character, double precision or
               integer SpiceCell.

               CSPICE provides the following macros, which declare and
               initialize the cell

                  SPICECHAR_CELL          ( a, ASZ, AMLEN );
                  SPICEDOUBLE_CELL        ( a, ASZ );
                  SPICEINT_CELL           ( a, ASZ );

               where ASZ is the maximum capacity of `a' and AMLEN is the
               maximum length of any member in the character cell.

   b           is a SPICE set, distinct from `a'.

               `b' must be declared as a SpiceCell of the same data type
               as `a'.

               CSPICE provides the following macros, which declare and
               initialize the cell

                  SPICECHAR_CELL          ( b, BSZ, BMLEN );
                  SPICEDOUBLE_CELL        ( b, BSZ );
                  SPICEINT_CELL           ( b, BSZ );

               where BSZ is the maximum capacity of `b' and BMLEN is the
               maximum length of any member in the character cell.

Detailed_Output

   c           is a SPICE set, distinct from sets `a' and `b', which
               contains the difference of `a' and `b' (that is, all of
               the elements which are in `a' but NOT in `b').

               When comparing elements of character sets, this routine
               ignores trailing blanks. Trailing blanks will be
               trimmed from the members of the output set `c'.

               `c' must be declared as a SpiceCell of the same data type
               as `a' and `b'.

               CSPICE provides the following macros, which declare and
               initialize the cell

                  SPICECHAR_CELL          ( c, CSZ, CMLEN );
                  SPICEDOUBLE_CELL        ( c, CSZ );
                  SPICEINT_CELL           ( c, CSZ );

               where CSZ is the maximum capacity of `c' and CMLEN is the
               maximum length of any member in the character cell.

Parameters

   None.

Exceptions

   1)  If the difference of the two sets contains more elements than can
       be contained in the output set, the error SPICE(SETEXCESS) is
       signaled by a routine in the call tree of this routine.

   2)  If the `a', `b' and `c' cell arguments are of type SpiceChar and
       the length of the elements of the output set is less than the
       maximum of the lengths of the elements of the input sets, the
       error SPICE(ELEMENTSTOOSHORT) is signaled by a routine in the
       call tree of this routine.

   3)  If the `a', `b' and `c' cell arguments do not have identical data
       types, the error SPICE(TYPEMISMATCH) is signaled.

   4)  If any of the `a', `b' or `c' cell arguments does not qualify as a
       SPICE set, the error SPICE(NOTASET) is signaled. SPICE sets
       have their data elements stored in increasing order and contain
       no duplicate elements.

   5)  If any of the `a', `b' or `c' cell arguments does not have a
       recognized data type, the error SPICE(NOTSUPPORTED) is signaled.

   6)  If the cell arguments are of type SpiceChar and the string length
       associated with any of them is non-positive or too short to be
       usable when constructing the equivalent SPICE character cells
       required by the wrapped SPICELIB routine, an error is signaled by
       a routine in the call tree of this routine.

Files

   None.

Particulars

   This is a generic SPICE set routine; it operates on sets of any
   supported data type.

   The difference of two sets contains every element which is
   in the first set, but NOT in the second.

         {a,b}      difference  {c,d}     =  {a,b}
         {a,b,c}                {b,c,d}      {a}
         {a,b,c,d}              {}           {a,b,c,d}
         {}                     {a,b,c,d}    {}
         {}                     {}           {}

Examples

   1) The following code fragment places the difference of the
      character sets planets and asteroids into the character set
      result.


         #include "SpiceUsr.h"
                .
                .
                .
         /.
         Declare the sets with string length NAMLEN and with maximum
         number of elements MAXSIZ.
         ./
         SPICECHAR_CELL ( planets,   MAXSIZ, NAMLEN );
         SPICECHAR_CELL ( asteroids, MAXSIZ, NAMLEN );
         SPICECHAR_CELL ( result,    MAXSIZ, NAMLEN );
                .
                .
                .
         /.
         Compute the difference.
         ./
         diff_c ( &planets, &asteroids, &result );


   2) Repeat example #1, this time using integer sets containing
      ID codes of the bodies of interest.


         #include "SpiceUsr.h"
                .
                .
                .
         /.
         Declare the sets with maximum number of elements MAXSIZ.
         ./
         SPICEINT_CELL ( planets,   MAXSIZ );
         SPICEINT_CELL ( asteroids, MAXSIZ );
         SPICEINT_CELL ( result,    MAXSIZ );
                .
                .
                .
         /.
         Compute the difference.
         ./
         diff_c ( &planets, &asteroids, &result );

Restrictions

   1)  The output set must be distinct from both of the input sets.
       For example, the following calls are invalid.

          diff_c  ( &current,  &new,      &current );
          diff_c  ( &new,      &current,  &current );

       In each of the examples above, whether or not the subroutine
       signals an error, the results will almost certainly be wrong.
       Nearly the same effect can be achieved, however, by placing the
       result into a temporary set, which is immediately copied back
       into one of the input sets, as shown below.

          diff_c  ( &current,  &new,  &temp );
          copy_c  ( &temp,     &new         );


   2)  String comparisons performed by this routine are Fortran-style:
       trailing blanks in the input sets are ignored. This gives
       consistent behavior with CSPICE code generated by the f2c
       translator, as well as with the Fortran SPICE Toolkit.

       Note that this behavior is not identical to that of the ANSI
       C library functions strcmp and strncmp.

Literature_References

   None.

Author_and_Institution

   N.J. Bachman        (JPL)
   C.A. Curzon         (JPL)
   J. Diaz del Rio     (ODC Space)
   W.L. Taber          (JPL)
   I.M. Underwood      (JPL)

Version

   -CSPICE Version 1.1.1, 29-OCT-2021 (JDR)

       Edited the header to comply with NAIF standard.

       Extended description of arguments "a", "b" and "c" to include
       type and preferred declaration method.

       Added entry #5 and #6 in -Exceptions section.

   -CSPICE Version 1.1.0, 15-FEB-2005 (NJB)

       Bug fix: loop bound changed from 2 to 3 in loop used
       to free dynamically allocated arrays.

   -CSPICE Version 1.0.0, 08-AUG-2002 (NJB) (CAC) (WLT) (IMU)

Index_Entries

   difference of two sets