varyinglength

Varyinglength refers to data elements whose size is not fixed in advance. In computing, the term describes values, records, or fields that can occupy different numbers of bytes depending on their content or context. Varyinglength contrasts with fixed-length representations where every element uses the same amount of space. Length information is typically stored alongside the value, either as a separate prefix, a delimiter, or as part of a structured header.

In data interchange and serialization, many formats use varyinglength fields to efficiently encode diverse data. Examples include length-prefixed strings, arrays encoded with a preceding length, and length-delimited messages in streaming protocols. Protocol buffers, CBOR, and MessagePack use variable-length encoding for certain types to reduce space for common small values. In databases and filesystems, variable-length records store only the used portion of a block, improving space utilization but complicating indexing and access patterns.

Data structures and algorithms are designed to handle varyinglength data. Dynamic arrays, linked lists, and rope data structures support operations on content whose length can change. For large text or binary blobs, a rope stores the content as a tree of shorter leaves, enabling efficient concatenation and substring operations despite varying lengths. In networking, frame-based or length-prefixed framing helps delimit messages of varying size over a continuous stream.

Challenges and trade-offs include overhead for length metadata, potential fragmentation, and parsing costs during access. Systems weigh the benefits of compactness against processing complexity and performance considerations.

Related concepts include variable-length encoding, length-prefix framing, and variable-length records.