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.
[edit]Requirements
The bitmask type supports a finite number of bitmask elements, which are distinct non-zero values of the bitmask type, such that, for any pairCi andCj,Ci& Ci is nonzero andCi& Cj is zero. In addition, the value0 is used to represent an empty bitmask, with no values set.
The bitwise operatorsoperator&,operator|,operator^,operator~,operator&=,operator|=, andoperator^= 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 anyBitmaskType:
| Expression | Meaning |
| X|= Y | sets the valueY in the objectX |
| X&= ~Y | clears the valueY in the objectX |
| X& Y | nonzero result indicates that the valueY is set in the objectX |
Each representable bitmask element is defined as aninline(since C++17)constexpr value of the bitmask type.
[edit]Standard library
The following standard library types satisfyBitmaskType:
Code that relies on some particular implementation option (e.g.int n=std::ios_base::hex) is non-portable becausestd::ios_base::fmtflags is not necessarily implicitly convertible toint.
