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STXXL
1.4.1
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STXXL
1.4.1
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STXXL has the restriction that the data types stored in the containers cannot have C/C++ pointers or references to other elements of external memory containers. The reason is that these pointers and references get invalidated when the blocks containing the elements they point/refer to are written to disk. To get around this problem, the links can be kept in the form of external memory iterators (e.g. stxxl::vector::iterator). The iterators remain valid while storing to and loading from the external memory. When dereferencing an external memory iterator, the pointed object is loaded from external memory by the library on demand (if the object is not in the cache of the data structure already).
STXXL containers differ from STL containers in treating allocation and distinguishing between uninitialized and initialized memory. STXXL containers assume that the data types they store are plain old data types (POD). The constructors and destructors of the contained data types are not called when a container changes its size. The support of constructors and destructors would imply a significant I/O cost penalty, e.g. on the deallocation of a non-empty container, one has to load all contained objects and call their destructors. This restriction sounds more severe than it is, since external memory data structures cannot cope with custom dynamic memory management anyway, which is the common use of custom constructors/destructors. However, we plan to implement special versions of STXXL containers which will support not only PODs, and handle construction/destruction appropriately.
STXXL library was designed to ease the access to external memory algorithms and data structures for a programmer. We decided to equip our implementations of out-of-memory data structure and algorithms with well known generic interfaces of internal memory data structures and algorithms from the Standard Template Library. Currently we have implementation of the following data structures (in STL terminology "containers"):
Beyond these, STXXL also provides a set of containers that are not part of the STL:
1.8.5 
