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.
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 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
n
inline
(since C++17)
constexpr
value of the bitmask type.
Standard library
The following standard library types satisfy
BitmaskType
:
Code that relies on some particular implementation option (e.g.
int
n
=
std::
ios_base
::
hex
) is non-portable because
std::ios_base::fmtflags
is not necessarily implicitly convertible to
int
.