# IROTData::GetComparisonData

Retrieves data from a moniker that can be used to test the moniker for equality against another moniker.

HRESULT GetComparisonData(

PVOID *ppvData, | //Indirect pointer to a buffer that receives the comparison data
ULONG cbMax, | //Length of buffer
PULONG pcbData | //Pointer to the length of the comparison data
); |

Parameters

ppvData
  [out] Indirect pointer to a buffer that receives the comparison data.
cbMax
  [in] Length of the buffer specified in ppvData.
pcbData
  [out] Pointer to the length of the comparison data.

Return Values

This method supports the standard return value E_OUTOFMEMORY, as well as the following:

S_OK
  The comparison data was successfully returned.

Remarks

The IROTData::GetComparisonData method is primarily called by the Running Object Table (ROT). The comparison data returned by the method is tested for binary equality against the comparison data returned by another moniker. The pcbData parameter enables the ROT to locate the end of the data returned.

#### Notes to Implementers

The comparison data that you return must uniquely identify the moniker, while still being as short as possible. The comparison data should include information about the internal state of the moniker, as well as the moniker’s CLSID. For example, the comparison data for a file moniker would include the path name stored within the moniker, as well as the CLSID of the file moniker implementation. This makes it possible to distinguish two monikers that happen to store similar state information but are instances of different moniker classes.

The comparison data for a moniker cannot exceed 2048 bytes in length. For composite monikers, the total length of the comparison data for all of its components cannot exceed 2048 bytes; consequently, if your moniker can be a component within a composite moniker, the comparison data you return must be significantly less than 2048 bytes.

If your comparison data is longer than the value specified by the cbMax parameter, you must return an error. Note that when IROTData::GetComparisionData is called on the components of a composite moniker, the value of cbMax becomes smaller for each moniker in sequence.

See Also

IMoniker, IRunningObjectTable