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create_vgroups.c

#include "hdf.h"

#define  FILE_NAME    "Two_Vgroups.hdf"

main()
{
   /************************* Variable declaration **************************/

   intn  status_n;      /* returned status for functions returning an intn  */
   int32 status_32,     /* returned status for functions returning an int32 */
         vgroup_ref = -1,
         vgroup1_id, vgroup2_id, file_id;

   /********************** End of variable declaration **********************/

   /*
   * Create the HDF file.
   */
   file_id = Hopen (FILE_NAME, DFACC_CREATE, 0);

   /*
   * Initialize the V interface.
   */
   status_n = Vstart (file_id);

   /*
   * Create the first vgroup.  Note that the vgroup reference number is set
   * to -1 for creating and the access mode is "w" for writing.
   */
   vgroup1_id = Vattach (file_id, vgroup_ref, "w");

   /*
   * Create the second vgroup. 
   */
   vgroup2_id = Vattach (file_id, vgroup_ref, "w");

   /*
   * Any operations on the vgroups.
   */

   /*
   * Terminate access to the first vgroup.
   */
   status_32 = Vdetach (vgroup1_id);

   /*
   * Terminate access to the second vgroup.
   */
   status_32 = Vdetach (vgroup2_id);

   /*
   * Terminate access to the V interface and close the HDF file.
   */
   status_n = Vend (file_id);
   status_n = Hclose (file_id);
}

create_vgroups.f

      program  create_vgroup
      implicit none
C
C     Parameter declaration
C
      character*15 FILE_NAME
C
      parameter (FILE_NAME = `Two_Vgroups.hdf')
      integer DFACC_CREATE
      parameter (DFACC_CREATE = 4)
C
C     Function declaration
C
      integer hopen, hclose
      integer vfstart, vfatch, vfdtch, vfend

C
C**** Variable declaration *******************************************
C
      integer status
      integer file_id
      integer vgroup1_id, vgroup2_id, vgroup_ref
C
C**** End of variable declaration ************************************
C
C
C     Create the HDF file.
C
      file_id = hopen(FILE_NAME, DFACC_CREATE, 0)
C
C     Initialize the V interface.
C
      status = vfstart(file_id)
C
C     Create the first vgroup. Note that the vgroup reference number is set
C     to -1 for creating and the access mode is `w' for writing.
C
      vgroup_ref = -1
      vgroup1_id = vfatch(file_id, vgroup_ref, `w')
C
C     Create the second vgroup.
C
      vgroup2_id = vfatch(file_id, vgroup_ref, `w')
C
C     Any operations on the vgroups.
C
C     ..............................
C
C     Terminate access to the first vgroup.
C
      status = vfdtch(vgroup1_id)
C
C     Terminate access to the second vgroup.
C
      status = vfdtch(vgroup2_id)
C
C     Terminate access to the V interface and close the HDF file.
C
      status = vfend(file_id)
      status = hclose(file_id)
      end

add_sds_to_vgroup.c

#include   "hdf.h"      /* Note: in this example, hdf.h can be omitted...*/
#include   "mfhdf.h"    /* ...since mfhdf.h already includes hdf.h */

#define  FILE_NAME    "General_Vgroups.hdf"
#define  SDS_NAME     "Test SD"
#define  VG_NAME      "SD Vgroup"
#define  VG_CLASS     "Common Vgroups"

main()
{
   /************************* Variable declaration **************************/

   intn   status_n;     /* returned status for functions returning an intn  */
   int32  status_32,    /* returned status for functions returning an int32 */
          sd_id,        /* SD interface identifier */
          sds_id,       /* data set identifier */
          sds_ref,      /* reference number of the data set */
          dim_sizes[1], /* dimension of the data set - only one */
          rank = 1,     /* rank of the data set array */
          vgroup_id,    /* vgroup identifier */
          file_id;      /* HDF file identifier, same for V interface */

   /********************** End of variable declaration **********************/

   /*
   * Create the HDF file.
   */
   file_id = Hopen (FILE_NAME, DFACC_CREATE, 0);

   /*
   * Initialize the V interface.
   */
   status_n = Vstart (file_id);

   /*
   * Initialize the SD interface.
   */
   sd_id = SDstart (FILE_NAME, DFACC_WRITE);

   /*
   * Set the size of the SDS's dimension.
   */
   dim_sizes[0] = 10;

   /*
   * Create the SDS.
   */
   sds_id = SDcreate (sd_id, SDS_NAME, DFNT_INT32, rank, dim_sizes);

   /*
   * Create a vgroup and set its name and class.
   */
   vgroup_id = Vattach (file_id, -1, "w");
   status_32 = Vsetname (vgroup_id, VG_NAME);
   status_32 = Vsetclass (vgroup_id, VG_CLASS);

   /*
   * Obtain the reference number of the SDS using its identifier.
   */
   sds_ref = SDidtoref (sds_id);

   /*
   * Add the SDS to the vgroup.  Note: the tag DFTAG_NDG is used
   * when adding an SDS.  Refer to Appendix A for the entire list of tags.
   */
   status_32 = Vaddtagref (vgroup_id, DFTAG_NDG, sds_ref);

   /*
   * Terminate access to the SDS and to the SD interface.
   */
   status_n = SDendaccess (sds_id);
   status_n = SDend (sd_id);

   /*
   * Terminate access to the vgroup and to the V interface, and 
   * close the HDF file.
   */
   status_32 = Vdetach (vgroup_id);
   status_n = Vend (file_id);
   status_n = Hclose (file_id);
}

add_sds_to_vgroup.f

      program  add_SDS_to_a_vgroup
      implicit none
C
C     Parameter declaration
C
      character*19 FILE_NAME
      character*7  SDS_NAME
      character*9  VG_NAME
      character*13 VG_CLASS
C
      parameter (FILE_NAME = `General_Vgroups.hdf',
     +           SDS_NAME  = `Test SD',
     +           VG_NAME   = `SD Vgroup',
     +           VG_CLASS  = `Common Vgroups')
      integer DFACC_CREATE, DFACC_WRITE 
      parameter (DFACC_CREATE = 4, DFACC_WRITE = 2)
      integer DFNT_INT32
      parameter (DFNT_INT32 = 24)
      integer DFTAG_NDG
      parameter (DFTAG_NDG = 720)
C
C     Function declaration
C
      integer hopen, hclose
      integer vfstart, vfatch, vfsnam, vfscls, vfadtr, vfdtch, vfend
      integer sfstart, sfcreate, sfid2ref, sfendacc, sfend

C
C**** Variable declaration *******************************************
C
      integer status
      integer file_id
      integer vgroup_id
      integer sd_id, sds_id, sds_ref
      integer dim_sizes(1), rank
C
C**** End of variable declaration ************************************
C
C
C     Create the HDF file.
C
      file_id = hopen(FILE_NAME, DFACC_CREATE, 0)
C
C     Initialize the V interface.
C
      status = vfstart(file_id)
       
C
C     Initialize SD interface. 
C
      sd_id = sfstart(FILE_NAME, DFACC_WRITE) 
C
C     Set the rank and the size of SDS's dimension.
C
      rank = 1
      dim_sizes(1) = 10
C
C     Create the SDS.
C
      sds_id = sfcreate(sd_id, SDS_NAME, DFNT_INT32, rank, dim_sizes)
C
C     Create a vgroup and set its name and class.
C
      vgroup_id = vfatch(file_id, -1 , `w')
      status    = vfsnam(vgroup_id, VG_NAME)
      status    = vfscls(vgroup_id, VG_CLASS)
C
C     Obtain the reference number of the SDS using its identifier.
C
      sds_ref = sfid2ref(sds_id)
C
C     Add the SDS to the vgroup. Note: the tag DFTAG_NDG is used
C     when adding an SDS.  Refer to HDF Reference Manual, Section III, Table 3K,
C     for the entire list of tags.
C
      status = vfadtr(vgroup_id, DFTAG_NDG, sds_ref)
C
C     Terminate access to the SDS and to the SD interface.
C
      status = sfendacc(sds_id)
      status = sfend(sd_id)
C
C     Terminate access to the vgroup.
C
      status = vfdtch(vgroup_id)
C
C     Terminate access to the V interface and close the HDF file.
C
      status = vfend(file_id)
      status = hclose(file_id)
      end

insert_vdatas_to_vgroup.c

#include "hdf.h"

#define  FILE_NAME         "General_Vgroups.hdf"
#define  N_RECORDS         30       /* number of records in the vdatas */
#define  ORDER             3        /* order of field FIELD_VD2 */
#define  VG_NAME           "Vertices"
#define  VG_CLASS          "Vertex Set"
#define  VD1_NAME          "X,Y Coordinates"   /* first vdata to hold X,Y...*/
#define  VD1_CLASS         "Position"          /*...values of the vertices */
#define  VD2_NAME          "Temperature"       /* second vdata to hold the...*/
#define  VD2_CLASS         "Property List"     /*...temperature field */
#define  VD3_NAME          "Node List"         /* third vdata to hold...*/
#define  VD3_CLASS         "Mesh"              /*...the list of nodes */
#define  FIELD1_VD1        "PX"    /* first field of first vdata - X values */
#define  FIELD2_VD1        "PY"/* second field of first vdata - Y values */
#define  FIELD_VD2         "TMP"/* field of third vdata */
#define  FIELD_VD3         "PLIST"/* field of second vdata */
#define  FIELDNAME_LIST    "PX,PY" /* field name list for first vdata */
/* Note that the second and third vdatas can use the field names as 
   the field name lists unless more fields are added to a vdata.
   Then a field name list is needed for that vdata */

main( )
{
   /************************* Variable declaration **************************/

   intn     status_n;   /* returned status for functions returning an intn  */
   int32    status_32,  /* returned status for functions returning an int32 */
            file_id, vgroup_id, 
            vdata1_id, vdata2_id, vdata3_id; 
   int32    num_of_records,           /* number of records actually written */
            vd_index;                 /* position of a vdata in the vgroup  */
   int8     i, j, k = 0;
   float32  pxy[N_RECORDS][2] =       /* buffer for data of the first vdata */
		  	{-1.5, 2.3, -1.5, 1.98, -2.4, .67,
   			-3.4, 1.46, -.65, 3.1, -.62, 1.23,
   			-.4, 3.8, -3.55, 2.3, -1.43, 2.44,
   			.23, 1.13, -1.4, 5.43, -1.4, 5.8,
   			-3.4, 3.85, -.55, .3, -.21, 1.22,
   			-1.44, 1.9, -1.4, 2.8, .94, 1.78,
   			-.4, 2.32, -.87, 1.99, -.54, 4.11,
   			-1.5, 1.35, -1.4, 2.21, -.22, 1.8,
   			-1.1, 4.55, -.44, .54, -1.11, 3.93,
   			-.76, 1.9, -2.34, 1.7, -2.2, 1.21};
   float32  tmp[N_RECORDS];          /* buffer for data of the second vdata */
   int16    plist[N_RECORDS][3];     /* buffer for data of the third vdata */

   /********************** End of variable declaration ***********************/

   /*
   * Open the HDF file for writing.
   */
   file_id = Hopen (FILE_NAME, DFACC_WRITE, 0);

   /*
   * Initialize the V interface.
   */
   status_n = Vstart (file_id);

   /*
   * Buffer the data for the second and third vdatas.
   */
   for (i = 0; i < N_RECORDS; i++)
      for (j = 0; j < ORDER; j++)
         plist[i][j] = ++k;

   for (i = 0; i < N_RECORDS; i++)
      tmp[i] = i * 10.0;

   /*
   * Create the vgroup then set its name and class.  Note that the vgroup's
   * reference number is set to -1 for creating and the access mode is "w" for
   * writing.
   */
   vgroup_id = Vattach (file_id, -1, "w");
   status_32 = Vsetname (vgroup_id, VG_NAME);
   status_32 = Vsetclass (vgroup_id, VG_CLASS);

   /*
   * Create the first vdata then set its name and class. Note that the vdata's
   * reference number is set to -1 for creating and the access mode is "w" for
   * writing.
   */
   vdata1_id = VSattach (file_id, -1, "w");
   status_32 = VSsetname (vdata1_id, VD1_NAME);
   status_32 = VSsetclass (vdata1_id, VD1_CLASS);

   /*
   * Introduce and define the fields of the first vdata.
   */
   status_n = VSfdefine (vdata1_id, FIELD1_VD1, DFNT_FLOAT32, 1);
   status_n = VSfdefine (vdata1_id, FIELD2_VD1, DFNT_FLOAT32, 1);
   status_n = VSsetfields (vdata1_id, FIELDNAME_LIST);

   /*
   * Write the buffered data into the first vdata with full interlace mode.
   */
   num_of_records = VSwrite (vdata1_id, (uint8 *)pxy, N_RECORDS, 
                             FULL_INTERLACE);

   /*
   * Insert the vdata into the vgroup using its identifier.
   */
   vd_index = Vinsert (vgroup_id, vdata1_id);

   /*
   * Detach from the first vdata.
   */
   status_32 = VSdetach (vdata1_id);

   /*
   * Create, write, and insert the second vdata to the vgroup using
   * steps similar to those used for the first vdata.
   */ 
   vdata2_id = VSattach (file_id, -1, "w");
   status_32 = VSsetname (vdata2_id, VD2_NAME);
   status_32 = VSsetclass (vdata2_id, VD2_CLASS);
   status_n = VSfdefine (vdata2_id, FIELD_VD2, DFNT_FLOAT32, 1);
   status_n = VSsetfields (vdata2_id, FIELD_VD2);
   num_of_records = VSwrite (vdata2_id, (uint8 *)tmp, N_RECORDS, 
                             FULL_INTERLACE);
   vd_index = Vinsert (vgroup_id, vdata2_id);
   status_32 = VSdetach (vdata2_id);

   /*
   * Create, write, and insert the third vdata to the vgroup using 
   * steps similar to those used for the first and second vdatas.
   */
   vdata3_id = VSattach (file_id, -1, "w");
   status_32 = VSsetname (vdata3_id, VD3_NAME);
   status_32 = VSsetclass (vdata3_id, VD3_CLASS);
   status_n = VSfdefine (vdata3_id, FIELD_VD3, DFNT_INT16, 3);
   status_n = VSsetfields (vdata3_id, FIELD_VD3);
   num_of_records = VSwrite (vdata3_id, (uint8 *)plist, N_RECORDS, 
                             FULL_INTERLACE);
   vd_index = Vinsert (vgroup_id, vdata3_id);
   status_32 = VSdetach (vdata3_id);

   /*
   * Terminate access to the vgroup "Vertices".
   */
   status_32 = Vdetach (vgroup_id);

   /*
   * Terminate access to the V interface and close the HDF file.
   */
   status_n = Vend (file_id);
   status_n = Hclose (file_id);
}

insert_vdatas_to_vgroup.f

      program  add_vdatas_to_a_vgroup
      implicit none
C
C     Parameter declaration
C
      character*19 FILE_NAME
      character*8  VG_NAME
      character*10 VG_CLASS
      character*15 VD1_NAME
      character*8  VD1_CLASS
      character*11 VD2_NAME
      character*13 VD2_CLASS
      character*9  VD3_NAME
      character*4  VD3_CLASS
C
      parameter (FILE_NAME = `General_Vgroups.hdf',
     +           VG_NAME   = `Vertices',
     +           VG_CLASS  = `Vertex Set')
      parameter (VD1_NAME  = `X,Y Coordinates',
     +           VD2_NAME  = `Temperature',
     +           VD3_NAME  = `Node List')
      parameter (VD1_CLASS = `Position',
     +           VD2_CLASS = `Property List',
     +           VD3_CLASS = `Mesh')
      character*2 FIELD1_VD1
      character*2 FIELD2_VD1
      character*3 FIELD_VD2
      character*4 FIELD_VD3
      character*5 FIELDNAME_LIST
      parameter (FIELD1_VD1 = `PX',
     +           FIELD2_VD1 = `PY',
     +           FIELD_VD2  = `TMP',
     +           FIELD_VD3  = `PLIST',
     +           FIELDNAME_LIST = `PX,PY')
      integer N_RECORDS
      parameter (N_RECORDS = 30)
      
      integer  DFACC_WRITE 
      parameter (DFACC_WRITE = 2)
      integer DFNT_FLOAT32, DFNT_INT16
      parameter (DFNT_FLOAT32 = 5, DFNT_INT16 = 22)
      integer FULL_INTERLACE 
      parameter (FULL_INTERLACE = 0)
C
C     Function declaration
C
      integer hopen, hclose
      integer vfstart, vfatch, vfsnam, vfscls, vfinsrt, vfdtch, vfend
      integer vsfatch, vsfsnam, vsfscls, vsffdef, vsfsfld, 
     +        vsfwrt, vsfwrtc, vsfdtch

C
C**** Variable declaration *******************************************
C
      integer status
      integer file_id
      integer vgroup_id
      integer vdata1_id, vdata2_id, vdata3_id, vd_index 
      integer num_of_records
      integer i, j, k
      real    pxy(2,N_RECORDS), tmp(N_RECORDS)
      integer plist(3,N_RECORDS)
      data pxy /-1.5, 2.3, -1.5, 1.98, -2.4, .67,
     +          -3.4, 1.46, -.65, 3.1, -.62, 1.23,
     +          -.4, 3.8, -3.55, 2.3, -1.43, 2.44,
     +          .23, 1.13, -1.4, 5.43, -1.4, 5.8,
     +          -3.4, 3.85, -.55, .3, -.21, 1.22,
     +          -1.44, 1.9, -1.4, 2.8, .94, 1.78,
     +          -.4, 2.32, -.87, 1.99, -.54, 4.11,
     +          -1.5, 1.35, -1.4, 2.21, -.22, 1.8,
     +          -1.1, 4.55, -.44, .54, -1.11, 3.93,
     +          -.76, 1.9, -2.34, 1.7, -2.2, 1.21/
C
C**** End of variable declaration ************************************
C
C
C     Open the HDF file for writing.
C
      file_id = hopen(FILE_NAME, DFACC_WRITE, 0)
C
C     Initialize the V interface.
C
      status = vfstart(file_id)
C
C     Buffer the data for the third and second vdatas.
C
      do 20 i = 1, N_RECORDS
         do 10 j = 1, 3 
            plist(j,i) = k 
            k = k+1
10       continue
20    continue    
      do 30 i = 1, N_RECORDS
         tmp(i) = (i-1) * 10.0
30    continue
C
C     Create a vgroup and set its name and class.
C     Note that the vgroup's reference number is set to -1 for creating
C     and the access mode is `w' for writing.
C
      vgroup_id = vfatch(file_id, -1 , `w')
      status    = vfsnam(vgroup_id, VG_NAME)
      status    = vfscls(vgroup_id, VG_CLASS)
C
C     Create the first vdata then set its name and class. Note that the vdata's
C     reference number is set to -1 for creating and the access mode is `w' for
C     writing.
C
      vdata1_id = vsfatch(file_id, -1, `w')
      status = vsfsnam(vdata1_id, VD1_NAME)
      status = vsfscls(vdata1_id, VD1_CLASS)
C
C     Introduce and define the fields of the first vdata.
C
      status = vsffdef(vdata1_id, FIELD1_VD1, DFNT_FLOAT32, 1)
      status = vsffdef(vdata1_id, FIELD2_VD1, DFNT_FLOAT32, 1)
      status = vsfsfld(vdata1_id, FIELDNAME_LIST)
C
C     Write the buffered data into the first vdata.
C
      num_of_records = vsfwrt(vdata1_id, pxy, N_RECORDS,
     +                        FULL_INTERLACE)
C
C     Insert the vdata into the vgroup using its identifier.
C
      vd_index = vfinsrt(vgroup_id, vdata1_id)
C
C     Detach from the first vdata.
C
      status = vsfdtch(vdata1_id)
C
C     Create, write, and insert the second vdata to the vgroup using
C     steps similar to those used for the first vdata.
C
      vdata2_id = vsfatch(file_id, -1, `w')
      status = vsfsnam(vdata2_id, VD2_NAME)
      status = vsfscls(vdata2_id, VD2_CLASS)
      status = vsffdef(vdata2_id, FIELD_VD2, DFNT_FLOAT32, 1)
      status = vsfsfld(vdata2_id, FIELD_VD2)
      num_of_records = vsfwrt(vdata2_id, tmp, N_RECORDS,
     +                        FULL_INTERLACE)
      vd_index = vfinsrt(vgroup_id, vdata2_id)
      status = vsfdtch(vdata2_id)
C
C     Create, write, and insert the third vdata to the vgroup using 
C     steps similar to those used for the first and second vdatas.
C
      vdata3_id = vsfatch(file_id, -1, `w')
      status = vsfsnam(vdata3_id, VD3_NAME)
      status = vsfscls(vdata3_id, VD3_CLASS)
      status = vsffdef(vdata3_id, FIELD_VD3, DFNT_INT16, 3)
      status = vsfsfld(vdata3_id, FIELD_VD3)
      num_of_records = vsfwrtc(vdata3_id, plist, N_RECORDS,
     +                        FULL_INTERLACE)
      vd_index = vfinsrt(vgroup_id, vdata3_id)
      status = vsfdtch(vdata3_id)
 
C
C     Terminate access to the vgroup `Vertices'.
C
      status = vfdtch(vgroup_id)
C
C     Terminate access to the V interface and close the HDF file.
C
      status = vfend(file_id)
      status = hclose(file_id)
      end

get_vgroup_info.c

#include "hdf.h"

#define  FILE_NAME   "General_Vgroups.hdf"

main( )
{
   /************************* Variable declaration **************************/

   intn   status_n;     /* returned status for functions returning an intn  */
   int32  status_32,    /* returned status for functions returning an int32 */
          file_id, vgroup_id;
   int32  lone_vg_number,      /* current lone vgroup number */
          num_of_lones = 0;    /* number of lone vgroups */
   int32 *ref_array;    /* buffer to hold the ref numbers of lone vgroups   */
   char   vgroup_name[VGNAMELENMAX], vgroup_class[VGNAMELENMAX];

   /********************** End of variable declaration **********************/
 
   /*
   * Open the HDF file for reading.
   */
   file_id = Hopen (FILE_NAME, DFACC_READ, 0); 

   /*
   * Initialize the V interface.
   */
   status_n = Vstart (file_id);

   /*
   * Get and print the names and class names of all the lone vgroups.
   * First, call Vlone with num_of_lones set to 0 to get the number of
   * lone vgroups in the file, but not to get their reference numbers.
   */
   num_of_lones = Vlone (file_id, NULL, num_of_lones );

   /*
   * Then, if there are any lone vgroups, 
   */
   if (num_of_lones > 0)
   {
      /*
      * use the num_of_lones returned to allocate sufficient space for the
      * buffer ref_array to hold the reference numbers of all lone vgroups,
      */
      ref_array = (int32 *) malloc(sizeof(int32) * num_of_lones);

      /*
      * and call Vlone again to retrieve the reference numbers into 
      * the buffer ref_array.
      */
      num_of_lones = Vlone (file_id, ref_array, num_of_lones);

      /*
      * Display the name and class of each lone vgroup.
      */
      printf ("Lone vgroups in this file are:\n");
      for (lone_vg_number = 0; lone_vg_number < num_of_lones; 
                                                            lone_vg_number++)
      {
         /*
         * Attach to the current vgroup then get and display its
         * name and class. Note: the current vgroup must be detached before
         * moving to the next.
         */
         vgroup_id = Vattach (file_id, ref_array[lone_vg_number], "r");
         status_32 = Vgetname (vgroup_id, vgroup_name);
         status_32 = Vgetclass (vgroup_id, vgroup_class);
         printf ("   Vgroup name %s and class %s\n", vgroup_name,  
                     vgroup_class); 
         status_32 = Vdetach (vgroup_id);
      } /* for */
   } /* if */

   /*
   * Terminate access to the V interface and close the file.
   */
   status_n = Vend (file_id);
   status_n = Hclose (file_id);

   /*
   * Free the space allocated by this program.
   */
   free (ref_array);
}

get_vgroup_info.f

      program  getinfo_about_vgroup
      implicit none
C
C     Parameter declaration
C
      character*19 FILE_NAME
C
      parameter (FILE_NAME = `General_Vgroups.hdf')
      integer DFACC_READ
      parameter (DFACC_READ = 1)
      integer SIZE
      parameter(SIZE = 10)
C
C     Function declaration
C
      integer hopen, hclose
      integer vfstart, vfatch, vfgnam, vfgcls, vflone, vfdtch, vfend

C
C**** Variable declaration *******************************************
C
      integer status
      integer file_id
      integer vgroup_id
      integer lone_vg_number, num_of_lones
      character*64 vgroup_name, vgroup_class
      integer ref_array(SIZE)
      integer i
C
C**** End of variable declaration ************************************
C
C
C     Initialize ref_array.
C
      do 10 i = 1, SIZE
         ref_array(i) = 0
10    continue
C
C     Open the HDF file for reading.
C
      file_id = hopen(FILE_NAME, DFACC_READ, 0)
C
C     Initialize the V interface.
C
      status = vfstart(file_id)
C
C     Get and print the name and class name of all lone vgroups.
C     First, call vflone with num_of_lones set to 0 to get the number of
C     lone vgroups in the file and check whether size of ref_array is 
C     big enough to hold reference numbers of ALL lone groups.
C     If ref_array is not big enough, exit the program after displaying an
C     informative message.
C
      num_of_lones = 0
      num_of_lones = vflone(file_id, ref_array, num_of_lones)
      if (num_of_lones .gt. SIZE) then
      write(*,*) num_of_lones, `lone vgroups is found'
      write(*,*) `increase the size of ref_array to hold reference `
      write(*,*) `numbers of all lone vgroups in the file'
      stop
      endif
C
C     If there are any lone groups in the file,
C
      if (num_of_lones .gt. 0) then
C
C     call vflone again to retrieve the reference numbers into ref_array.
C
      num_of_lones = vflone(file_id, ref_array, num_of_lones)
C
C     Display the name and class of each vgroup.
C
      write(*,*) `Lone vgroups in the file are:'

      do 20 lone_vg_number = 1, num_of_lones
C
C     Attach to the current vgroup, then get and display its name and class.
C     Note: the current vgroup must be detached before moving to the next.  
C
      vgroup_name = ` `
      vgroup_class = ` `
      vgroup_id = vfatch(file_id, ref_array(lone_vg_number), `r')
      status    = vfgnam(vgroup_id, vgroup_name)
      status    = vfgcls(vgroup_id, vgroup_class)
      write(*,*) `Vgroup name ` ,  vgroup_name
      write(*,*) `Vgroup class ` , vgroup_class
      write(*,*)
      status = vfdtch(vgroup_id)
20    continue

      endif
C
C     Terminate access to the V interface and close the HDF file.
C
      status = vfend(file_id)
      status = hclose(file_id)
      end

set_get_vgroup_attr.c

#include "hdf.h"

#define  FILE_NAME      "General_Vgroups.hdf"
#define  VGROUP_NAME    "SD Vgroup"
#define  VGATTR_NAME    "First Attribute"
#define  N_ATT_VALUES   7              /* number of values in the attribute */

main( )
{
   /************************* Variable declaration **************************/

   intn   status_n,     /* returned status for functions returning an intn  */
          n_attrs;      /* number of attributes of the vgroup */
   int32  status_32,    /* returned status for functions returning an int32 */
          file_id, vgroup_ref, vgroup_id,
          attr_index, i, vg_version,
          data_type, n_values, size;
   char   vg_attr[N_ATT_VALUES] = {`v','g','r','o','u','p','\0'};
   char   vgattr_buf[N_ATT_VALUES], attr_name[30];

   /********************** End of variable declaration **********************/

   /*
   * Open the HDF file for writing.
   */
   file_id = Hopen (FILE_NAME, DFACC_WRITE, 0);

   /*
   * Initialize the V interface.
   */
   status_n = Vstart (file_id);

   /*
   * Get the reference number of the vgroup named VGROUP_NAME.
   */
   vgroup_ref = Vfind (file_id, VGROUP_NAME);

   /*
   * Attach to the vgroup found.
   */
   vgroup_id = Vattach (file_id, vgroup_ref, "w");

   /*
   * Get and display the version of the attached vgroup.
   */
   vg_version = Vgetversion (vgroup_id);
   switch (vg_version) {
        case VSET_NEW_VERSION:
              printf ("\nVgroup %s is of the newest version, version 4\n", 
                   VGROUP_NAME);
           break;
        case VSET_VERSION:
              printf ("Vgroup %s is of a version between 3.2 and 4.0r2\n", 
                   VGROUP_NAME);
           break;
        case VSET_OLD_VERSION:
              printf ("Vgroup %s is of version before 3.2\n", VGROUP_NAME);
           break;
        default:
           printf ("Unknown version = %d\n", vg_version);
        } /* switch */

   /*
   * Add the attribute named VGATTR_NAME to the vgroup.
   */
   status_n = Vsetattr (vgroup_id, VGATTR_NAME, DFNT_CHAR, N_ATT_VALUES, 
                        vg_attr);

   /*
   * Get and display the number of attributes attached to this vgroup.
   */
   n_attrs = Vnattrs (vgroup_id);
   printf ("\nThis vgroup has %d attribute(s)\n", n_attrs);

   /*
   * Get and display the name and the number of values of each attribute.
   * Note that the fourth and last parameters are set to NULL because the type 
   * and the size of the attribute are not desired.
   */
   for (attr_index = 0; attr_index < n_attrs; attr_index++)
   {
      status_n = Vattrinfo (vgroup_id, attr_index, attr_name, NULL, 
                            &n_values, NULL);
      printf ("\nAttribute #%d is named %s and has %d values: ",
                            attr_index+1, attr_name, n_values);

      /*
      * Get and display the attribute values.
      */
      status_n = Vgetattr (vgroup_id, attr_index, vgattr_buf);
      for (i = 0; i < n_values; i++)
         printf ("%c ", vgattr_buf[i]);
      printf ("\n");
   }


   /*
   * Terminate access to the vgroup and to the V interface, and close 
   * the HDF file.
   */
   status_32 = Vdetach (vgroup_id);
   status_n = Vend (file_id);
   status_n = Hclose (file_id);
}


set_get_vgroup_attr.f

      program  vgroup_attribute
      implicit none
C
C     Parameter declaration
C
      character*19 FILE_NAME
      character*9  VGROUP_NAME
      character*15 VGATTR_NAME
C
      parameter (FILE_NAME    = `General_Vgroups.hdf',
     +           VGROUP_NAME  = `SD Vgroup',
     +           VGATTR_NAME  = `First Attribute')
      integer VSET_NEW_VERSION, VSET_VERSION, VSET_OLD_VERSION
      parameter (VSET_NEW_VERSION = 4,
     +           VSET_VERSION     = 3,
     +           VSET_OLD_VERSION = 2)  
      integer DFACC_WRITE 
      parameter (DFACC_WRITE = 2)
      integer DFNT_CHAR
      parameter (DFNT_CHAR = 4)
      integer N_ATT_VALUES
      parameter (N_ATT_VALUES = 6)
C
C     Function declaration
C
      integer hopen, hclose
      integer vfstart, vfatch, vfgver, vfscatt, vfnatts, vfainfo,
     +        vfind, vfgcatt, vfdtch, vfend
C
C**** Variable declaration *******************************************
C
      integer status, n_attrs
      integer file_id
      integer vgroup_id, vgroup_ref, vg_version
      integer attr_index, i
      integer data_type, n_values, size 
      character vg_attr(N_ATT_VALUES)
      character vgattr_buf(N_ATT_VALUES), attr_name(30)
      data vg_attr /'v','g','r','o','u','p'/
C
C**** End of variable declaration ************************************
C
C
C     Open the HDF file for reading/writing.
C
      file_id = hopen(FILE_NAME, DFACC_WRITE, 0)
C
C     Initialize the V interface.
C
      status = vfstart(file_id)
C
C     Get the reference number of the vgroup named VGROUP_NAME.
C
      vgroup_ref = vfind(file_id, VGROUP_NAME)
C
C     Attach to the vgroup found.
C
      vgroup_id = vfatch(file_id, vgroup_ref , `w')
C
C     Get and display the version of the attached vgroup.
C
      vg_version = vfgver(vgroup_id)
      if (vg_version .eq. VSET_NEW_VERSION) write(*,*)
     +   VGROUP_NAME, ` is of the newest version, version 4'
      if (vg_version .eq. VSET_VERSION) write(*,*)
     +   VGROUP_NAME, ` is of a version between 3.2 and 4.0r2'
      if(vg_version .eq. VSET_OLD_VERSION) write(*,*)
     +   VGROUP_NAME, ` is of version before 3.2'
      if ((vg_version .ne. VSET_NEW_VERSION) .and.
     +    (vg_version .ne. VSET_VERSION)     .and.
     +    (vg_version .ne. VSET_OLD_VERSION)) write(*,*)   
     +    `Unknown version'
C
C     Add the attribute named VGATTR_NAME to the vgroup.
C
      status = vfscatt(vgroup_id, VGATTR_NAME, DFNT_CHAR, N_ATT_VALUES,
     +                 vg_attr)
C
C     Get and display the number of attributes attached to this group.
C
      n_attrs = vfnatts(vgroup_id)
      write(*,*) `This group has', n_attrs, ` attributes'
C
C     Get and display the name and the number of values of each attribute.
C
      do 10 attr_index=1, n_attrs
         status = vfainfo(vgroup_id, attr_index-1, attr_name, data_type,
     +                    n_values, size)
      write(*,*) `Attribute #', attr_index-1, ` is named `, attr_name
      write(*,*) `and has', n_values, ` values: `
C
C     Get and display the attribute values.
C
      status = vfgcatt(vgroup_id, attr_index-1, vgattr_buf)
      write(*,*) (vgattr_buf(i), i=1,n_values)
10    continue
C
C     Terminate access to the vgroup.
C
      status = vfdtch(vgroup_id)
C
C     Terminate accessto the V interface and close the HDF file.
C
      status = vfend(file_id)
      status = hclose(file_id)
      end

vgroup_contents.c

#include "hdf.h"

#define   FILE_NAME        "General_Vgroups.hdf"

main( )
{
   /************************* Variable declaration **************************/

   intn   status_n;     /* returned status for functions returning an intn  */
   int32  status_32,    /* returned status for functions returning an int32 */
          file_id, vgroup_id, vgroup_ref,
          obj_index,    /* index of an object within a vgroup */
          num_of_pairs, /* number of tag/ref number pairs, i.e., objects */
          obj_tag, obj_ref,     /* tag/ref number of an HDF object */
          vgroup_pos = 0;       /* position of a vgroup in the file */

   /********************** End of variable declaration ***********************/

   /*
   * Open the HDF file for reading.
   */
   file_id = Hopen (FILE_NAME, DFACC_READ, 0);

   /*
   * Initialize the V interface.
   */
   status_n = Vstart (file_id);

   /*
   * Obtain each vgroup in the file by its reference number, get the
   * number of objects in the vgroup, and display the information about
   * that vgroup.
   */
   vgroup_ref = -1;        /* set to -1 to search from the beginning of file */
   while (TRUE)
   {
      /*
      * Get the reference number of the next vgroup in the file.
      */
      vgroup_ref = Vgetid (file_id, vgroup_ref);

      /*
      * Attach to the vgroup for reading or exit the loop if no more vgroups
      * are found.
      */
      if (vgroup_ref == -1) break;
      vgroup_id = Vattach (file_id, vgroup_ref, "r"); 

      /*
      * Get the total number of objects in the vgroup.
      */
      num_of_pairs = Vntagrefs (vgroup_id);

      /*
      * If the vgroup contains any object, print the tag/ref number 
      * pair of each object in the vgroup, in the order they appear in the
      * file, and indicate whether the object is a vdata, vgroup, or neither.
      */
      if (num_of_pairs > 0)
      {
         printf ("\nVgroup #%d contains:\n", vgroup_pos);
         for (obj_index = 0; obj_index < num_of_pairs; obj_index++)
         {
            /*
            * Get the tag/ref number pair of the object specified 
            * by its index, obj_index, and display them.
            */
            status_n = Vgettagref (vgroup_id, obj_index, &obj_tag, &obj_ref);
            printf ("tag = %d, ref = %d", obj_tag, obj_ref);

            /*
            * State whether the HDF object referred to by obj_ref is a vdata,
            * a vgroup, or neither.
            */
            if (Visvg (vgroup_id, obj_ref))
               printf ("  <-- is a vgroup\n");
            else if (Visvs (vgroup_id, obj_ref))
               printf ("  <-- is a vdata\n");
            else
               printf ("  <-- neither vdata nor vgroup\n");
         } /* for */
      } /* if */

      else
         printf ("Vgroup #%d contains no HDF objects\n", vgroup_pos);

      /*
      * Terminate access to the current vgroup.
      */
      status_32 = Vdetach (vgroup_id);

      /*
      * Move to the next vgroup position.
      */
      vgroup_pos++;
   } /* while */

   /*
   * Terminate access to the V interface and close the file.
   */
   status_n = Vend (file_id);
   status_n = Hclose (file_id);
}

vgroup_contents.f

      program  vgroup_contents
      implicit none
C
C     Parameter declaration
C
      character*19 FILE_NAME
C
      parameter (FILE_NAME = `General_Vgroups.hdf')
      integer DFACC_ READ
      parameter (DFACC_READ = 1)
C
C     Function declaration
C
      integer hopen, hclose
      integer vfstart, vfatch, vfgid, vntrc, vfgttr, vfisvg,
     +        vfisvs, vfdtch, vfend

C
C**** Variable declaration *******************************************
C
      integer status
      integer file_id
      integer vgroup_id, vgroup_ref,  vgroup_pos
      integer obj_index, num_of_pairs 
      integer obj_tag, obj_ref 
C
C**** End of variable declaration ************************************
C
C
C     Open the HDF file for reading.
C
      file_id = hopen(FILE_NAME, DFACC_READ, 0)
C
C     Initialize the V interface.
C
      status = vfstart(file_id)
C
C     Obtain each vgroup in the file by its reference number, get the
C     number of objects in the vgroup, and display the information
C     about that vgroup.
C
      vgroup_ref = -1
      vgroup_pos = 0
10    continue
C
C     Get the reference number of the next vgroup in the file.
C
      vgroup_ref = vfgid(file_id, vgroup_ref)
C
C     Attach to the vgroup or go to the end if no additional vgroup is found.
C
      if(vgroup_ref. eq. -1) goto 100
      vgroup_id = vfatch(file_id, vgroup_ref , `r')
C
C     Get the total number of objects in the vgroup.
C
      num_of_pairs = vntrc(vgroup_id)
C
C     If the vgroup contains any object, print the tag/ref number
C     pair of each object in vgroup, in the order they appear in the
C     file, and indicate whether the object is a vdata, vgroup, or neither.
C
      if (num_of_pairs .gt. 0) then
         write(*,*) `Vgroup # `, vgroup_pos, ` contains:'
         do 20 obj_index = 1, num_of_pairs
C
C     Get the tag/ref number pair of the object specified by its index 
C     and display them.
C
         status = vfgttr(vgroup_id, obj_index-1, obj_tag, obj_ref)
C
C     State whether the HDF object referred to by obj_ref is a vdata,
C     a vgroup, or neither.
C
         if( vfisvg(vgroup_id, obj_ref) .eq. 1) then
             write(*,*) `tag = `, obj_tag, ` ref = `, obj_ref,
     +       `  <--- is a vgroup `
         else if ( vfisvs(vgroup_id, obj_ref) .eq. 1) then
             write(*,*) `tag = `, obj_tag, ` ref = `, obj_ref,
     +       `  <--- is a vdata `
         else
             write(*,*) `tag = `, obj_tag, ` ref = `, obj_ref,
     +       `  <--- neither vdata nor vgroup `
         endif
20       continue
      else
         write (*,*) `Vgroup #', vgroup_pos, ` contains no HDF objects'
      endif
      write(*,*)
      vgroup_pos = vgroup_pos + 1
      goto 10 
100   continue      
C
C     Terminate access to the vgroup.
C
      status = vfdtch(vgroup_id)
C
C     Terminate access to the V interface and close the HDF file.
C
      status = vfend(file_id)
      status = hclose(file_id)
      end




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HDF User's Guide - 05/19/99, NCSA HDF Development Group.