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[class.static.data]

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- ### Static data members <a id="class.static.data">[[class.static.data]]</a>
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- A `static` data member is not part of the subobjects of a class. If a
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- `static` data member is declared `thread_local` there is one copy of the
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- member per thread. If a `static` data member is not declared
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  `thread_local` there is one copy of the data member that is shared by
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  all the objects of the class.
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- The declaration of a `static` data member in its class definition is not
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- a definition and may be of an incomplete type other than cv-qualified
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- `void`. The definition for a `static` data member shall appear in a
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- namespace scope enclosing the member’s class definition. In the
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- definition at namespace scope, the name of the `static` data member
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- shall be qualified by its class name using the `::` operator. The
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- *initializer* expression in the definition of a `static` data member is
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- in the scope of its class ([[basic.scope.class]]).
 
 
 
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  ``` cpp
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  class process {
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  static process* run_chain;
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  static process* running;
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  process* process::running = get_main();
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  process* process::run_chain = running;
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  ```
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- The `static` data member `run_chain` of class `process` is defined in
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  global scope; the notation `process::run_chain` specifies that the
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  member `run_chain` is a member of class `process` and in the scope of
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- class `process`. In the `static` data member definition, the
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- *initializer* expression refers to the `static` data member `running` of
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- class `process`.
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-
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- Once the `static` data member has been defined, it exists even if no
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- objects of its class have been created. in the example above,
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- `run_chain` and `running` exist even if no objects of class `process`
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- are created by the program.
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-
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- If a non-volatile `const` `static` data member is of integral or
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- enumeration type, its declaration in the class definition can specify a
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- *brace-or-equal-initializer* in which every *initializer-clause* that is
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- an *assignment-expression* is a constant expression ([[expr.const]]). A
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- `static` data member of literal type can be declared in the class
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- definition with the `constexpr` specifier; if so, its declaration shall
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- specify a *brace-or-equal-initializer* in which every
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- *initializer-clause* that is an *assignment-expression* is a constant
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- expression. In both these cases, the member may appear in constant
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- expressions. The member shall still be defined in a namespace scope if
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- it is odr-used ([[basic.def.odr]]) in the program and the namespace
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- scope definition shall not contain an *initializer*.
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-
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- There shall be exactly one definition of a `static` data member that is
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- odr-used ([[basic.def.odr]]) in a program; no diagnostic is required.
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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  Unnamed classes and classes contained directly or indirectly within
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- unnamed classes shall not contain `static` data members.
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- `Static` data members of a class in namespace scope have external
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- linkage ([[basic.link]]). A local class shall not have `static` data
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- members.
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- `Static` data members are initialized and destroyed exactly like
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- non-local variables ([[basic.start.init]],  [[basic.start.term]]).
 
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- A `static` data member shall not be `mutable` ([[dcl.stc]]).
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+ #### Static data members <a id="class.static.data">[[class.static.data]]</a>
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+ A static data member is not part of the subobjects of a class. If a
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+ static data member is declared `thread_local` there is one copy of the
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+ member per thread. If a static data member is not declared
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  `thread_local` there is one copy of the data member that is shared by
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  all the objects of the class.
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+ The declaration of a non-inline static data member in its class
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+ definition is not a definition and may be of an incomplete type other
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+ than cv `void`. The definition for a static data member that is not
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+ defined inline in the class definition shall appear in a namespace scope
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+ enclosing the member’s class definition. In the definition at namespace
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+ scope, the name of the static data member shall be qualified by its
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+ class name using the `::` operator. The *initializer* expression in the
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+ definition of a static data member is in the scope of its class (
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+ [[basic.scope.class]]).
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+
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+ [*Example 1*:
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  ``` cpp
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  class process {
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  static process* run_chain;
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  static process* running;
 
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  process* process::running = get_main();
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  process* process::run_chain = running;
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  ```
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+ The static data member `run_chain` of class `process` is defined in
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  global scope; the notation `process::run_chain` specifies that the
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  member `run_chain` is a member of class `process` and in the scope of
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+ class `process`. In the static data member definition, the *initializer*
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+ expression refers to the static data member `running` of class
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+ `process`.
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+
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+ — *end example*]
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+
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+ [*Note 1*:
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+
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+ Once the static data member has been defined, it exists even if no
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+ objects of its class have been created.
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+
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+ [*Example 2*:
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+
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+ In the example above, `run_chain` and `running` exist even if no objects
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+ of class `process` are created by the program.
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+
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+ — *end example*]
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+
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+ — *end note*]
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+
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+ If a non-volatile non-inline `const` static data member is of integral
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+ or enumeration type, its declaration in the class definition can specify
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+ a *brace-or-equal-initializer* in which every *initializer-clause* that
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+ is an *assignment-expression* is a constant expression (
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+ [[expr.const]]). The member shall still be defined in a namespace scope
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+ if it is odr-used ([[basic.def.odr]]) in the program and the namespace
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+ scope definition shall not contain an *initializer*. An inline static
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+ data member may be defined in the class definition and may specify a
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+ *brace-or-equal-initializer*. If the member is declared with the
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+ `constexpr` specifier, it may be redeclared in namespace scope with no
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+ initializer (this usage is deprecated; see [[depr.static_constexpr]]).
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+ Declarations of other static data members shall not specify a
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+ *brace-or-equal-initializer*.
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+
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+ [*Note 2*: There shall be exactly one definition of a static data
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+ member that is odr-used ([[basic.def.odr]]) in a program; no diagnostic
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+ is required. — *end note*]
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+
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  Unnamed classes and classes contained directly or indirectly within
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+ unnamed classes shall not contain static data members.
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+ [*Note 3*: Static data members of a class in namespace scope have the
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+ linkage of that class ([[basic.link]]). A local class cannot have
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+ static data members ([[class.local]]). — *end note*]
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+ Static data members are initialized and destroyed exactly like non-local
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+ variables ([[basic.start.static]], [[basic.start.dynamic]],
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+ [[basic.start.term]]).
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+ A static data member shall not be `mutable` ([[dcl.stc]]).
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