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1.3 The Vgroup API

The Vgroup interface consists of routines for accessing, creating and getting information about vgroups.

1.3.1 Vgroup Library Routines

Vgroup API routine names are prefaced by "V". These routines are categorized as follows:

The Vgroup API routines, along with the two H interface routines used to open and close HDF files for vgroup access, are listed in Table 5A below.

TABLE 5A Vgroup Interface Routines
Category

Routine Name

Description

C

Fortran-77

Access

Vstart

vfstart

Initializes the V interface.

Vattach

vfatch

Establishes access to a vgroup.

Vdetach

vsfdtch

Terminates access to a vgroup.

Vend

vfend

Terminates access to the V interface.

Create

Vsetclass

vfscls

Assigns a class to a vgroup.

Vsetname

vfsnam

Assigns a name to a vgroup.

Vinsert

vfinsrt

Adds a vgroup or vdata to an existing vgroup.

Vaddtagref

vfadtr

Adds any HDF data object to an existing vgroup.

Vsetattr

vfsnatt/vfscatt

Sets the attribute of a vgroup.

File Inquiry

Vlone

vflone

Returns the reference numbers of vgroups not included in other vgroups.

Vgetid

vfgid

Returns the reference number for the next vgroup in the HDF file.

Vgroup Inquiry

Vinquire

vfinq

Returns general information about a vgroup.

Vgetclass

vfgcls

Returns the class of the specified vgroup.

Vgetname

vfgnam

Returns the name of the specified vgroup.

Visvg

vfisvg

Checks if a vgroup identifier belongs to a vgroup within a vgroup.

Visvs

vfisvs

Checks if a vdata identifier belongs to a vdata within a vgroup.

Vgettagref

vfgttr

Retrieves a tag/ reference number pair for a data object in the specified vgroup.

Vntagrefs

vfntr

Returns the number of tag/reference number pairs contained in the specified vgroup.

Vgetnext

vfgnxt

Returns the identifier of the next vgroup or vdata in a vgroup.

Vgettagrefs

vfgttrs

Retrieves the tag/reference pairs of all of the data objects with a vgroup.

Vinqtagref

vfinqtr

Checks if an object belongs to a vgroup.

Vgetversion

None

Queries the vgroup version of a given vgroup.

Vnaattrs

vfnatts

Queries the total number of vgroup attributes.

Vfindattr

vffdatt

Retrieves the index of an attribute given the attribute name.

Vattrinfo

vfainfo

Queries information on a given vgroup attribute.

Vgetattr

vfgnatt/vfgcatt

Queries the values of a given attribute.

1.3.2 Vgroup Identifiers in the Vgroup Interface

The Vgroup interface identifies vgroups in several ways. Before a vgroup is attached, it is uniquely identified by its name, class and reference number. When a vgroup is attached, it is assigned a vgroup identifier or vgroup id. After a vgroup has been attached, its vgroup id is used by the Vgroup interface routines to access vgroups.

The name, class, and reference number are values assigned to the vgroup when it is created. The name and class are normally assigned by the calling program and may be changed throughout the scope of the vgroup object. However, the reference number is assigned by the HDF library and not changed.



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HDF User's Guide - 06/04/97, NCSA HDF Development Group.