Flagfield

Flagfield is a data field designed to store multiple boolean attributes compactly by packing them into individual bits within a fixed-size integer or bitset. It is used in software design, databases, and network protocols to represent a set of on/off flags without reserving separate boolean bytes for each attribute.

Common implementations include language-level bitfields, such as C/C++ bit-field structs, or application-level schemes that use an integer or bitset where each bit corresponds to a flag. A typical scheme reserves bit 0 for 'active', bit 1 for 'admin', bit 2 for 'verified', etc. The exact mapping is defined by a flag mask constant or enumeration.

Operations on a flagfield involve bitwise manipulation: setting a flag by OR-ing with a mask, clearing by AND-ing with the negated mask, toggling by XOR-ing, and testing by AND-ing and comparing to zero. In databases, a flagfield may be implemented as a tiny integer type or a dedicated bit type, with application logic mapping bits to attributes.

Advantages include reduced memory usage and improved cache performance when many flags are stored per record. Drawbacks include reduced readability and maintainability, potential portability concerns across platforms and languages, and the need for careful documentation of bit mappings. Overuse can also lead to errors in interpretation of bits.

Flagfields are common in embedded systems, file formats, and network protocols where compact encoding of attributes is important. They are also used in software to minimize the size of status fields in large records or logs.