A Preprocessor Approach to Persistent C++

Abstract

In conventional object oriented programming languages, objects are transient, that is they are destroyed upon program termination. Storing objects using explicit file access methods may cause objects to lose their manipulation and access semantics since the objects with different declarations may have the same storage representation. In this work persistence is added to C++ in DOS environment through a preprocessor and a class library developed in C++, such that the access and manipulation semantics of objects are preserved. The new language is called C**. The disk management of objects declared as persistent are automatically handled by the system through a virtual memory management emulation. Persistency is implemented as a storage class that is completely orthogonal to type. In other words, persistency is a property of objects, not their classes. Language changes are kept to a minimum, thus among the existing persistent C++ implementations, C** requires the minimum coding effort. Furthermore objects of any complexity with arbitrary level of pointer indirections to any type of object is supported. As a result, objects are stored on disk as they are represented in memory. Upward compatibility with C++ is preserved. The hybrid object identifier (OID) mechanism implemented in C** enables dynamic clustering and reduction in the object table size. Although there are several other persistent C++ implementations, the implementation technique of C** is original in that it provides the user with transparent type modifications and uses operator overloading extensively in realizing persistency. To the best of our knowledge C** is the first persistent C++ implementation on DOS with persistence as a storage class.