19.8.1. Bit-fields
A class can define a (nonstatic) data member as a bit-field. A bit-field holds a specified number of bits. Bit-fields are normally used when a program needs to pass binary data to another program or to a hardware device.
Note
The memory layout of a bit-field is machine dependent.
A bit-field must have integral or enumeration type (§ 19.3, p. 832). Ordinarily, we use an unsigned type to hold a bit-field, because the behavior of a signed bit-field is implementation defined. We indicate that a member is a bit-field by following the member name with a colon and a constant expression specifying the number of bits:
typedef unsigned ...
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