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What Is a CArchive Object 

A CArchive object provides a type-safe buffering mechanism for writing or reading serializable objects to or from a CFile object. Usually the CFile object represents a disk file; however, it can also be a memory file (CSharedFile object), perhaps representing the Clipboard.

A given CArchive object either stores (writes, serializes) data or loads (reads, deserializes) data, but never both. The life of a CArchive object is limited to one pass through writing objects to a file or reading objects from a file. Thus, two successively created CArchive objects are required to serialize data to a file and then deserialize it back from the file.

When an archive stores objects to a file, the archive attaches the CRuntimeClass name to the objects. Then, when another archive loads objects from a file to memory, the CObject-derived objects are dynamically reconstructed based on the CRuntimeClass of the objects. A given object may be referenced more than once as it is written to the file by the storing archive. The loading archive, however, will reconstruct the object only once. The details about how an archive attaches CRuntimeClass information to objects and reconstructs objects, taking into account possible multiple references, are described in Technical Note 2.

As data is serialized to an archive, the archive accumulates the data until its buffer is full. Then the archive writes its buffer to the CFile object pointed to by the CArchive object. Similarly, as you read data from an archive, it reads data from the file to its buffer and then from the buffer to your deserialized object. This buffering reduces the number of times a hard disk is physically read, thus improving your application's performance.

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