fixedformat

Fixedformat, or fixed-format, refers to a data layout in which a record is composed of fields that occupy fixed, predefined positions and widths within each line or block. In a fixed-format file, each field starts at a known offset and ends after a predetermined number of characters or bytes. There are no delimiters between fields; the schema defines where each field begins and ends. This approach contrasts with delimited formats (such as CSV or TSV) and with variable-length records.

Key characteristics include a stable record length and a schema-driven interpretation of the data. Field definitions are typically documented in a separate specification or a copybook in COBOL environments, detailing the exact start position and length for every field. The data may be stored in text or binary form, and in historical contexts, fixed-format layouts were common in mainframe and midrange systems. Some legacy systems use fixed-length records to maximize speed and simplicity in batch processing, reporting, and data interchange.

Advantages of fixed-format data include predictable parsing, efficient sequential reads, straightforward offsets for random access within a record, and strong compatibility with languages that can slice strings by position. Disadvantages include inflexibility to schema changes, potential waste of space for short fields, lack of self-describing structure, and brittle adaptability when records vary in length or when auxiliary metadata is needed.

Typical use cases involve legacy financial and administrative systems, mainframe data transfers, and environments where performance and deterministic structure are prioritized over human readability. Modern data workflows may convert fixed-format data to more flexible forms (such as CSV or JSON) for analysis, integration, or archival.