# IMoniker::CommonPrefixWith

Creates a new moniker based on the common prefix that this moniker (the one comprising the data of this moniker object) shares with another moniker.

HRESULT CommonPrefixWith(

IMoniker *pmkOther, | //Pointer to moniker to be used for comparison
IMoniker **ppmkPrefix | //Indirect pointer to the prefix
); |

Parameters

pmkOther
  [in] Pointer to the IMoniker interface on another moniker to be compared with this one to determine whether there is a common prefix.
ppmkPrefix
  [out] When successful, points to the IMoniker pointer to the moniker that is the common prefix of this moniker and pmkOther. In this case, the implementation must call IUnknown::AddRef on the parameter; it is the caller’s responsibility to call IUnknown::Release. If an error occurs or if there is no common prefix, the implementation should set ppmkPrefix to NULL.

Return Values

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

S_OK
  A common prefix exists that is neither this moniker nor pmkOther.
MK_S_NOPREFIX
  No common prefix exists.
MK_S_HIM
  The entire pmkOther moniker is a prefix of this moniker.
MK_S_US
  The two monikers are identical.
MK_S_ME
  This moniker is a prefix of the pmkOther moniker.
MK_E_NOTBINDABLE
  This method was called on a relative moniker. It is not meaningful to take the common prefix on a relative moniker.

Remarks

IMoniker::CommonPrefixWith creates a new moniker that consists of the common prefixes of the moniker on this moniker object and another moniker. If, for example, one moniker represents the path “c:\projects\secret\art\pict1.bmp” and another moniker represents the path “c:\projects\secret\docs\chap1.txt,” the common prefix of these two monikers would be a moniker representing the path “c:\projects\secret.”

#### Notes to Callers

The IMoniker::CommonPrefixWith method is primarily called in the implementation of the IMoniker::RelativePathTo method. Clients using a moniker to locate an object rarely need to call this method.

Call this method only if pmkOther and this moniker are both absolute monikers. An absolute moniker is either a file moniker or a generic composite whose leftmost component is a file moniker that represents an absolute path. Do not call this method on relative monikers, because it would not produce meaningful results.

#### Notes to Implementers

Your implementation should first determine whether pmkOther is a moniker of a class that you recognize and for which you can provide special handling (for example, if it is of the same class as this moniker). If so, your implementation should determine the common prefix of the two monikers. Otherwise, it should pass both monikers in a call to the MonikerCommonPrefixWith function, which correctly handles the generic case.

See Also

IMoniker::RelativePathTo, MonikerCommonPrefixWith