variablelength

Variable length refers to data elements whose size can vary, as opposed to fixed-length elements. It is used to optimize storage and transmission by allocating only as much space as needed for each value. The concept appears in data formats, programming languages, databases, and communications protocols.

In data formats, fields may be stored with a length prefix or a delimiter to indicate the size of the subsequent data. Length-prefix encoding is common in binary formats; for example, a length field precedes a string or a record. Delimiter-based schemes use characters or byte sequences to separate items, such as in CSV. Variable-length strings and arrays are standard in many languages, with memory managed dynamically or via dynamic data structures.

A family of schemes known as variable-length quantity and varint encodes integers using a minimal number of bytes; high-order bits indicate continuation. These are used in MIDI, ASN.1/BER, Google's Protocol Buffers, and other protocols to save space for small values.

In databases, variable-length columns such as VARCHAR or TEXT store their content with associated length information; record layouts may mix fixed- and variable-length fields. Benefits include space efficiency and flexibility; downsides include parsing overhead and potential fragmentation. The choice between fixed and variable length depends on access patterns and storage constraints.