IOleUndoManager::DiscardFrom method (ocidl.h)

Article
02/22/2024

Instructs the undo manager to discard the specified undo unit and all undo units below it on the undo or redo stack.

Syntax

HRESULT DiscardFrom(
  [in] IOleUndoUnit *pUU
);

Parameters

[in] pUU

An IOleUndoUnit pointer to the undo unit to be discarded. This parameter can be NULL to discard the entire undo or redo stack. If the parameter is not NULL then the stack will not be discarded.

Return value

This method returns S_OK on success. Other possible return values include the following.

Return code	Description
E_INVALIDARG	The specified undo unit was not found in the stacks.
E_UNEXPECTED	The undo manager is disabled.

Remarks

The undo manager first searches the undo stack for the given unit, and if not found there searches the redo stack. After it has been found, the given unit and all below it on the same stack are discarded. The undo unit may be a child of a parent unit contained by the undo manager, as determined by calling IOleParentUndoUnit::FindUnit. If it is a child unit, then the root unit containing the given unit and all units below it on the appropriate stack are discarded.

If there is an open parent unit and the DiscardFrom method is called and the pUU parameter is NULL, the undo manager should immediately release and discard the open parent unit without calling the IOleUndoManager::Close first. When the object that opened the parent unit attempts to close it, IOleUndoManager::Close will return S_FALSE. If a parent unit is open, throw it away and discard the stack. If the parent unit is not open, just throw the stack away. If the pUU parameter is not NULL, then any open parent units should be left open.

Requirements

Requirement	Value
Minimum supported client	Windows 2000 Professional [desktop apps only]
Minimum supported server	Windows 2000 Server [desktop apps only]
Target Platform	Windows
Header	ocidl.h