Example 6. Obtaining Information about the Contents of a Vgroup

This example illustrates the use of Vgetid/vfgid to get the reference number
of a vgroup, Vntagrefs/vntrc to get the number of HDF objects in the vgroup,
Vgettagref/vfgttr to get the tag/reference number pair of an object within the
vgroup, and Visvg/vfisvg and Visvs/vfisvs to determine whether an object
is a vgroup and a vdata, respectively.

In the example, the program traverses the HDF file
"General_Vgroups.hdf" from the beginning and obtains the reference
number of each vgroup so it can be attached.  Once a vgroup is
attached, the program gets the total number of tag/reference number
pairs in the vgroup and displays some information about the vgroup.
The information displayed includes the position of the vgroup in the
file, the tag/reference number pair of each of its objects, and the
message stating whether the object is a vdata, vgroup, or neither. 
