STXXL  1.4.1
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Serializing Variable Data Structures with binary_buffer

Some applications of STXXL will require variable data structures. Currently there is not much support for this in STXXL.

For serializing information into in-memory data blocks, the STXXL provides the helper classes binary_buffer and binary_reader. These provide functions binary_buffer::put<>() to append arbitrary integral data types and binary_reader::get<>() to read these again. Serialization and deserialization of variable data structures are then composed of identical sequences of put()/get().

Additionally, the classes already provide methods to serialize variable length strings (together with their lengths), and thereby also sub-block serialization. These functions are called binary_buffer::put_string() and binary_reader::get_string().

Furthermore, to squeeze small integers into fewer bytes, they classes also contain "varint" encoding, where each byte contains 7 data bits and one continuation bit. These functions are called binary_buffer::put_varint() and binary_reader::get_varint().

The following example fills a binary_buffer with some data elements:

// construct a binary blob
bb.put<unsigned int>(1);
// add a sub block
sub.put_string("sub block");
sub.put_varint(6 * 9);

And the following binary_reader example deserializes the data elements and check's their content.

// read binary block using binary_reader
STXXL_CHECK(br.get<unsigned int>() == 1);
STXXL_CHECK(br.get_string() == "test");
STXXL_CHECK(br.get_varint() == 42);
STXXL_CHECK(br.get_varint() == 12345678);
STXXL_CHECK(sub_br.get_string() == "sub block");
STXXL_CHECK(sub_br.get_varint() == 6 * 9);