Defines a type that can be used to represent a set of constant values or any combination of those values. This trait is typically implemented by integer types, std::bitset
, or enumerations (scoped and unscoped) with additional operator overloads.
The bitmask type supports a finite number of bitmask elements, which are distinct non-zero values of the bitmask type, such that, for any pair Ci
and Cj
, Ci & Ci
is nonzero and Ci & Cj
is zero. In addition, the value 0
is used to represent an empty bitmask, with no values set.
The bitwise operators operator&
, operator|
, operator^
, operator~
, operator&=
, operator|=
, and operator^=
are defined for values of the bitmask type and have the same semantics as the corresponding built-in operators on unsigned integers would have if the bitmask elements were the distinct integer powers of two.
The following expressions are well-formed and have the following meaning for any BitmaskType:
X |= Y | sets the value Y in the object X |
X &= ~Y | clears the value Y in the object X |
X & Y | nonzero result indicates that the value Y is set in the object X |
Each representable bitmask element is defined as a inline
(since C++17)constexpr
value of the bitmask type.
The following standard library types satisfy BitmaskType:
std::chars_format
(since C++17) std::ctype_base::mask
std::ios_base::fmtflags
std::ios_base::iostate
std::ios_base::openmode
std::regex_traits::char_class_type
(since C++11) std::regex_constants::syntax_option_type
(since C++11) std::regex_constants::match_flag_type
(since C++11) std::launch
(since C++11) std::filesystem::perms
(since C++17) std::filesystem::perm_options
(since C++17) std::filesystem::copy_options
(since C++17) std::filesystem::directory_options
(since C++17) Code that relies on some particular implementation option (e.g. int n = std::ios_base::hex
), is nonportable because std::ios_base::fmtflags
is not necessarily implicitly convertible to int
.
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https://en.cppreference.com/w/cpp/named_req/BitmaskType