IRootStorage::SwitchToFile method (objidl.h)

Article
06/09/2021

The SwitchToFile method copies the current file associated with the storage object to a new file. The new file is then used for the storage object and any uncommitted changes.

Syntax

HRESULT SwitchToFile(
  LPOLESTR pszFile
);

Parameters

pszFile

A pointer to a null terminated string that specifies the file name for the new file. It cannot be the name of an existing file. If NULL, this method creates a temporary file with a unique name, and you can call IStorage::Stat to retrieve the name of the temporary file.

Return value

This method can return one of these values.

Return code	Description
S_OK	The file was successfully copied.
STG_E_MEDIUMFULL	The file was not copied because of insufficient space on the storage device.
STG_E_ACCESSDENIED	The file was not copied because the caller does not have permission to access storage device.
STG_E_INVALIDPOINTER	The file was not copied because the pszFile pointer is not valid.
STG_E_FILEALREADYEXISTS	The file was not copied because the new filename (pszFile) points to an existing file.

Remarks

The IRootStorage::SwitchToFile method copies the file associated with the storage object. A COM container calls SwitchToFile to perform a full save on a file in a low-memory situation. Typically, this is done only after a normal, full save operation (that is, save to temporary file, delete original file, rename temporary file) has failed with an E_OUTOFMEMORY error.

It is erroneous to call the SwitchToFile method if the storage object or anything contained within it has been marshaled to another process. Before calling SwitchToFile, the container must call the IPersistStorage::HandsOffStorage method for any element within the storage object that is loaded or running. The HandsOffStorage method forces the element to release its storage pointers and enter the hands-off storage mode. The container must also release all pointers to streams or storages that are contained in this root storage. After the full save operation is completed, the container returns the contained elements to normal storage mode.

Notes to Implementers

If you are implementing your own storage objects, the IRootStorage methods (including QueryInterface, AddRef, and Release) must not consume additional memory or file handles.

Requirements

Requirement	Value
Minimum supported client	Windows 2000 Professional [desktop apps \| UWP apps]
Minimum supported server	Windows 2000 Server [desktop apps \| UWP apps]
Target Platform	Windows
Header	objidl.h
Library	Uuid.lib
DLL	Ole32.dll

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