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IStorage interface

The IStorage interface supports the creation and management of structured storage objects. Structured storage allows hierarchical storage of information within a single file, and is often referred to as "a file system within a file". Elements of a structured storage object are storages and streams. Storages are analogous to directories, and streams are analogous to files. Within a structured storage there will be a primary storage object that may contain substorages, possibly nested, and streams. Storages provide the structure of the object, and streams contain the data, which is manipulated through the IStream interface.

The IStorage interface provides methods for creating and managing the root storage object, child storage objects, and stream objects. These methods can create, open, enumerate, move, copy, rename, or delete the elements in the storage object.

An application must release its IStorage pointers when it is done with the storage object to deallocate memory used. There are also methods for changing the date and time of an element.

There are a number of different modes in which a storage object and its elements can be opened, determined by setting values from STGM Constants. One aspect of this is how changes are committed. You can set direct mode, in which changes to an object are immediately written to it, or transacted mode, in which changes are written to a buffer until explicitly committed. The IStorage interface provides methods for committing changes and reverting to the last-committed version. For example, a stream can be opened in read-only mode or read/write mode. For more information, see STGM Constants.

Other methods provide access to information about a storage object and its elements through the STATSTG structure.

When to implement

Generally, you would not implement this interface unless you were defining a new storage scheme for your system. COM provides a compound file implementation of the IStorage interface that supports transacted access. COM provides a set of helper APIs to facilitate using the compound file implementation of storage objects. For more information, see IStorage - Compound File Implementation.

When to use

Call the methods of IStorage to manage substorages or streams within the current storage. This management includes creating, opening, or destroying substorages or streams, as well as managing aspects such as time stamps, names, and so forth. You also can commit changes or revert to previous version for storages opened in transacted mode. The methods of IStorage do not include means to read and write data—this is reserved for IStream, which manages the actual data. While the IStorage and IStream interfaces are used to manipulate the storage object and its elements, the IPersistStorage interface contains methods that are called to serialize the storage object and its elements to a disk file.

Members

The IStorage interface inherits from the IUnknown interface. IStorage also has these types of members:

Methods

The IStorage interface has these methods.

MethodDescription
Commit

Reflects changes for a transacted storage object to the parent level.

CopyTo

Copies the entire contents of this open storage object into another storage object. The layout of the destination storage object may differ.

CreateStorage

Creates and opens a new storage object within this storage object. The name must not exceed 31 characters in length (not including the string terminator). The 000 through 01f characters, serving as the first character of the stream/storage name, are reserved for use by OLE. This is a compound file restriction, not a structured storage restriction.

CreateStream

Creates and opens a stream object with the specified name contained in this storage object. The name must not exceed 31 characters in length (not including the string terminator). The 000 through 01f characters, serving as the first character of the stream/storage name, are reserved for use by OLE. This is a compound file restriction, not a structured storage restriction.

DestroyElement

Removes the specified storage or stream from this storage object.

EnumElements

Returns an enumerator object that can be used to enumerate the storage and stream objects contained within this storage object.

MoveElementTo

Copies or moves a substorage or stream from this storage object to another storage object.

OpenStorage

Opens an existing storage object with the specified name according to the specified access mode. The name must not exceed 31 characters in length (not including the string terminator). The 000 through 01f characters, serving as the first character of the stream/storage name, are reserved for use by OLE. This is a compound file restriction, not a structured storage restriction.

OpenStream

Opens an existing stream object within this storage object using the specified access permissions in grfMode. The name must not exceed 31 characters in length (not including the string terminator). The 000 through 01f characters, serving as the first character of the stream/storage name, are reserved for use by OLE. This is a compound file restriction, not a structured storage restriction.

RenameElement

Renames the specified storage or stream in this storage object.

Revert

Discards all changes that have been made to the storage object since the last commit operation.

SetClass

Assigns the specified CLSID to this storage object.

SetElementTimes

Sets the modification, access, and creation times of the indicated storage element, if supported by the underlying file system.

SetStateBits

Stores up to 32 bits of state information in this storage object.

Stat

Returns the STATSTG structure for this open storage object.

 

Requirements

Minimum supported client

Windows 2000 Professional [desktop apps | Windows Store apps]

Minimum supported server

Windows 2000 Server [desktop apps | Windows Store apps]

Header

Objidl.h

IDL

Objidl.idl

Library

Uuid.lib

DLL

Ole32.dll

IID

IID_IStorage is defined as 0000000B-0000-0000-C000-000000000046

See also

EnumAll Sample
Samples

 

 

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