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Standard C Implementation Definition
B.1.9
Structures, unions, enumerations, and bitfields
The ISO/IEC C standard requires the following implementation details to be
documented for structured data types:
• the outcome when a member of a union is accessed using a member of different
type
• the padding and alignment of members of structures
• whether a plain int bitfield is treated as a signed int bitfield or as an unsigned int
bitfield
• the order of allocation of bitfields within a unit
• whether a bitfield can straddle a storage-unit boundary
• the integer type chosen to represent the values of an enumeration type.
See Chapter 5 C and C++ Implementation Details for more information.
Unions
See Unions on page 5-7 for information.
Enumerations
See Enumerations on page 5-7 for information.
Padding and alignment of structures
See Structures on page 5-8 for information.
Bitfields
See Bitfields on page 5-10 for information.
B.1.10
Qualifiers
An object that has a volatile-qualified type is accessed as a word, halfword, or byte as
determined by its size and alignment. For volatile objects larger than a word, the order
of accesses to the parts of the object is undefined. Updates to volatile bitfields generally
require a read-modify-write. Accesses to aligned word, halfword and byte types are
atomic. Other volatile accesses are not necessarily atomic.
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