bitfield

A bitfield is a sequence of bits used to store small values more compactly than standard integers. Bitfields can be realized as fields within a larger integer value, or as members of a struct in languages such as C and C++. Each field reserves a fixed number of bits.

In C and C++, a bit-field is declared by specifying a width after a colon, for example: struct Flags { unsigned int a:1; unsigned int b:2; unsigned int c:3; }; This tells the compiler how many bits to use for each member.

The layout and packing of bit-fields are implementation-defined and may vary between compilers and targets. In many environments, bit-fields map directly to hardware registers or protocol fields. The address of a bit-field is not always obtainable, and operations on bit-fields may incur non-trivial costs.

Common uses include compact storage of flags or small integers and mapping to hardware registers or binary file formats. Reading and modifying bit-fields usually involves masks and bitwise operators, or direct field access if supported by the compiler. Endianness can affect multi-byte fields.

Advantages include space efficiency and straightforward hardware mapping; disadvantages include portability concerns and potential non-portable layout. Bit-fields are not always suitable for portable I/O or serialization. Alternatives include using integers with explicit masks, or higher-level abstractions such as bitset.