IEnumFORMATETC

IEnumFORMATETC is a COM interface in Microsoft's Component Object Model (COM) that enumerates a sequence of FORMATETC structures. A FORMATETC structure, in turn, describes the format of data for a data transfer operation, such as copying and pasting or drag-and-drop.

The primary purpose of IEnumFORMATETC is to allow an object to provide a list of the data formats it supports to another object. This is crucial for enabling interoperability between different applications or components that need to exchange data. For example, when a user copies data from one application to the clipboard, the source application might provide an IEnumFORMATETC interface that lists the various formats the data can be represented in (e.g., text, rich text, images, etc.). The destination application can then query this interface to determine which formats it can paste.

The interface defines methods for iterating through the available formats. The most important of these is the Next method, which retrieves a specified number of FORMATETC structures from the enumeration. Other methods include Skip, which advances the enumeration by a specified number of elements, and Reset, which returns the enumeration to the beginning. Clone allows for the creation of a new enumerator that has the same enumeration state as the current one.

Implementations of IEnumFORMATETC are typically provided by objects that are sources of data for transfers. These objects use the interface to advertise their capabilities to potential data recipients, facilitating flexible and robust data exchange within the Windows environment.