Postfix expressions group left-to-right.

[Note 1:

The > token following the type-id in a dynamic_cast, static_cast, reinterpret_cast, or const_cast can be the product of replacing a >> token by two consecutive > tokens ([temp.names]).

— end note]

A subscript expression is a postfix expression followed by square brackets containing a possibly empty, comma-separated list of initializer-clauses that constitute the arguments to the subscript operator.

The postfix-expression and the initialization of the object parameter ([dcl.fct]) of any applicable subscript operator function ([over.sub]) is sequenced before each expression in the expression-list and also before any default argument ([dcl.fct.default]).

The initialization of a non-object parameter of a subscript operator function S, including every associated value computation and side effect, is indeterminately sequenced with respect to that of any other non-object parameter of S.

With the built-in subscript operator, an expression-list shall be present, consisting of a single assignment-expression.

One of the expressions shall be a glvalue of type “array of T” or a prvalue of type “pointer to T” and the other shall be a prvalue of unscoped enumeration or integral type.

The result is of type “T”.

The type “T” shall be a completely-defined object type.44

The expression E1[E2] is identical (by definition) to *((E1)+(E2)), except that in the case of an array operand, the result is an lvalue if that operand is an lvalue and an xvalue otherwise.

[Note 1:

Despite its asymmetric appearance, subscripting is a commutative operation except for sequencing.

See [expr.unary] and [expr.add] for details of * and + and [dcl.array] for details of array types.

— end note]

A function call is a postfix expression followed by parentheses containing a possibly empty, comma-separated list of initializer-clauses which constitute the arguments to the function.

The postfix expression shall have function type or function pointer type.

For a call to a non-member function or to a static member function, the postfix expression shall be either an lvalue that refers to a function (in which case the function-to-pointer standard conversion ([conv.func]) is suppressed on the postfix expression), or a prvalue of function pointer type.

If the selected function is non-virtual, or if the id-expression in the class member access expression is a qualified-id, that function is called.

Otherwise, its final overrider in the dynamic type of the object expression is called; such a call is referred to as a virtual function call.

[Note 3:

If a function name is used, and name lookup does not find a declaration of that name, the program is ill-formed.

No function is implicitly declared by such a call.

— end note]

If the postfix-expression names a destructor or pseudo-destructor ([expr.prim.id.dtor]), the type of the function call expression is void; otherwise, the type of the function call expression is the return type of the statically chosen function (i.e., ignoring the virtual keyword), even if the type of the function actually called is different.

If the postfix-expression names a pseudo-destructor (in which case the postfix-expression is a possibly-parenthesized class member access), the function call destroys the object of scalar type denoted by the object expression of the class member access ([expr.ref], [basic.life]).

A type is call-compatible with a function type if is the same type as or if the type “pointer to ” can be converted to type “pointer to ” via a function pointer conversion ([conv.fctptr]).

Calling a function through an expression whose function type is not call-compatible with the type of the called function's definition results in undefined behavior.

If the function is an explicit object member function and there is an implied object argument ([over.call.func]), the list of provided arguments is preceded by the implied object argument for the purposes of this correspondence.

If there is no corresponding argument, the default argument for the parameter is used.

If the function is an implicit object member function, the object expression of the class member access shall be a glvalue and the implicit object parameter of the function ([over.match.funcs]) is initialized with that glvalue, converted as if by an explicit type conversion.

When a function is called, the type of any parameter shall not be a class type that is either incomplete or abstract.

It is implementation-defined whether a parameter is destroyed when the function in which it is defined exits ([stmt.return], [except.ctor], [expr.await]) or at the end of the enclosing full-expression; parameters are always destroyed in the reverse order of their construction.

The initialization and destruction of each parameter occurs within the context of the full-expression ([intro.execution]) where the function call appears.

The postfix-expression is sequenced before each expression in the expression-list and any default argument.

The initialization of a parameter or, if the implementation introduces any temporary objects to hold the values of function parameters ([class.temporary]), the initialization of those temporaries, including every associated value computation and side effect, is indeterminately sequenced with respect to that of any other parameter.

These evaluations are sequenced before the evaluation of the precondition assertions of the function, which are evaluated in sequence ([dcl.contract.func]).

For any temporaries introduced to hold the values of function parameters, the initialization of the parameter objects from those temporaries is indeterminately sequenced with respect to the evaluation of each precondition assertion.

The result of a function call is the result of the possibly-converted operand of the return statement ([stmt.return]) that transferred control out of the called function (if any), except in a virtual function call if the return type of the final overrider is different from the return type of the statically chosen function, the value returned from the final overrider is converted to the return type of the statically chosen function.

When the called function exits normally ([stmt.return], [expr.await]), all postcondition assertions of the function are evaluated in sequence ([dcl.contract.func]).

If the implementation introduces any temporary objects to hold the result value as specified in [class.temporary], the evaluation of each postcondition assertion is indeterminately sequenced with respect to the initialization of any of those temporaries or the result object.

These evaluations, in turn, are sequenced before the destruction of any function parameters.

[Note 9:

A function can change the values of its non-const parameters, but these changes cannot affect the values of the arguments except where a parameter is of a reference type ([dcl.ref]); if the reference is to a const-qualified type, const_cast needs to be used to cast away the constness in order to modify the argument's value.

In addition, it is possible to modify the values of non-constant objects through pointer parameters.

— end note]

A function can be declared to accept fewer arguments (by declaring default arguments) or more arguments (by using the ellipsis, ..., or a function parameter pack ([dcl.fct])) than the number of parameters in the function definition.

When there is no parameter for a given argument, the argument is passed in such a way that the receiving function can obtain the value of the argument by invoking va_arg ([support.runtime]).

An argument that has type cv std​::​nullptr_t is converted to type void* ([conv.ptr]).

After these conversions, if the argument does not have arithmetic, enumeration, pointer, pointer-to-member, or class type, the program is ill-formed.

Passing a potentially-evaluated argument of a scoped enumeration type ([dcl.enum]) or of a class type ([class]) having an eligible non-trivial copy constructor ([special], [class.copy.ctor]), an eligible non-trivial move constructor, or a non-trivial destructor ([class.dtor]), with no corresponding parameter, is conditionally-supported with implementation-defined semantics.

If the argument has integral or enumeration type that is subject to the integral promotions, or a floating-point type that is subject to the floating-point promotion, the value of the argument is converted to the promoted type before the call.

These promotions are referred to as the default argument promotions.

A function call is an lvalue if the result type is an lvalue reference type or an rvalue reference to function type, an xvalue if the result type is an rvalue reference to object type, and a prvalue otherwise.

If it is a non-void prvalue, the type of the function call expression shall be complete, except as specified in [dcl.type.decltype].

A postfix expression followed by a dot . or an arrow ->, optionally followed by the keyword template, and then followed by an id-expression or a splice-expression, is a postfix expression.

For a dot that is followed by an expression that designates a static member or an enumerator, the first expression is a discarded-value expression ([expr.context]); if the expression after the dot designates a non-static data member ([class.mem.general]) or a direct base class relationship ([class.derived.general]), the first expression shall be a glvalue.

A postfix expression that is followed by an arrow shall be a prvalue having pointer type.

The expression E1->E2 is converted to the equivalent form (*(E1)).E2; the remainder of [expr.ref] will address only the form using a dot.45

The postfix expression before the dot is evaluated;46 the result of that evaluation, together with the id-expression or splice-expression, determines the result of the entire postfix expression.

If the object expression is of scalar type, E2 shall name the pseudo-destructor of that same type (ignoring cv-qualifications) and E1.E2 is a prvalue of type “function of () returning void”.

Otherwise, the object expression shall be of class type.

The class type shall be complete unless the class member access appears in the definition of that class.

E2 shall designate either a member of T1 or a direct base class relationship (T1, B).

If E2 designates a bit-field, E1.E2 is a bit-field.

The type and value category of E1.E2 are determined as follows.

In the remainder of [expr.ref], cq represents either const or the absence of const and vq represents either volatile or the absence of volatile.

If E2 designates an entity that is declared to have type “reference to T”, then E1.E2 is an lvalue of type T.

In that case, if E2 designates a static data member, E1.E2 designates the object or function to which the reference is bound, otherwise E1.E2 designates the object or function to which the corresponding reference member of E1 is bound.

Otherwise, one of the following rules applies.

• If E2 designates a static data member and the type of E2 is T, then E1.E2 is an lvalue; the expression designates the named member of the class.

  The type of E1.E2 is T.

• Otherwise, if E2 designates a non-static data member and the type of E1 is “cq1 vq1 X”, and the type of E2 is “cq2 vq2 T”, the expression designates the corresponding member subobject of the object designated by E1.

  If E1 is an lvalue, then E1.E2 is an lvalue; otherwise E1.E2 is an xvalue.

  Let the notation vq12 stand for the “union” of vq1 and vq2; that is, if vq1 or vq2 is volatile, then vq12 is volatile.

  Similarly, let the notation cq12 stand for the “union” of cq1 and cq2; that is, if cq1 or cq2 is const, then cq12 is const.

  If the entity designated by E2 is declared to be a mutable member, then the type of E1.E2 is “vq12 T”.

  If the entity designated by E2 is not declared to be a mutable member, then the type of E1.E2 is “cq12 vq12 T”.

• Otherwise, if E2 denotes an overload set, the expression shall be the (possibly-parenthesized) left-hand operand of a member function call ([expr.call]), and function overload resolution ([over.match]) is used to select the function to which E2 refers.

  The type of E1.E2 is the type of E2 and E1.E2 refers to the function referred to by E2.

  • If E2 refers to a static member function, E1.E2 is an lvalue.

  • Otherwise (when E2 refers to a non-static member function), E1.E2 is a prvalue.

    [Note 5:

    Any redundant set of parentheses surrounding the expression is ignored ([expr.prim.paren]).

    — end note]

• Otherwise, if E2 designates a nested type, the expression E1.E2 is ill-formed.

• Otherwise, if E2 designates a member enumerator and the type of E2 is T, the expression E1.E2 is a prvalue of type T whose value is the value of the enumerator.

• Otherwise, if E2 designates a direct base class relationship and D is either the cv-unqualified class type of E1 or a base class thereof, let cv be the cv-qualification of the type of E1.

  E1 is implicitly converted to the type “reference to cv D” (where the reference is an lvalue reference if E1 is an lvalue and an rvalue reference otherwise) and the expression designates the direct base class subobject of type B of the object designated by the converted E1.

  If E1 is an lvalue, then E1.E2 is an lvalue; otherwise, E1.E2 is an xvalue.

  The type of E1.E2 is cv B.

  [Example 1: struct B { int b; }; struct C : B { int get() const { return b; } }; struct D : B, C { }; constexpr int f() { D d = {1, {}}; B& b = d.[: std::meta::bases_of(^^D, std::meta::access_context::current())[0] :]; b.b += 10; return 10 * b.b + d.get(); } static_assert(f() == 110); — end example]

• Otherwise, the program is ill-formed.

If E2 designates a non-static member (possibly after overload resolution), the program is ill-formed if the class of which E2 designates a direct member is an ambiguous base ([class.member.lookup]) of the designating class ([class.access.base]) of E2.

If E2 designates a non-static member (possibly after overload resolution) or direct base class relationship and the result of E1 is an object whose type is not similar ([conv.qual]) to the type of E1, the behavior is undefined.

The value of a postfix ++ expression is the value obtained by applying the lvalue-to-rvalue conversion ([conv.lval]) to its operand.

The operand shall be a modifiable lvalue.

The type of the operand shall be an arithmetic type other than cv bool, or a pointer to a complete object type.

The value of the operand object is modified ([defns.access]) as if it were the operand of the prefix ++ operator ([expr.pre.incr]).

The value computation of the ++ expression is sequenced before the modification of the operand object.

With respect to an indeterminately-sequenced function call, the operation of postfix ++ is a single evaluation.

The result is a prvalue.

The type of the result is the cv-unqualified version of the type of the operand.

The operand of postfix -- is decremented analogously to the postfix ++ operator.

The result of the expression dynamic_cast<T>(v) is the result of converting the expression v to type T.

T shall be a pointer or reference to a complete class type, or “pointer to cv void”.

The dynamic_cast operator shall not cast away constness ([expr.const.cast]).

If T is a pointer type, v shall be a prvalue of a pointer to complete class type, and the result is a prvalue of type T.

If T is an lvalue reference type, v shall be an lvalue of a complete class type, and the result is an lvalue of the type referred to by T.

If T is an rvalue reference type, v shall be a glvalue having a complete class type, and the result is an xvalue of the type referred to by T.

If the type of v is the same as T (ignoring cv-qualifications), the result is v (converted if necessary).

If T is “pointer to cv1 B” and v has type “pointer to cv2 D” such that B is a base class of D, the result is a pointer to the unique B subobject of the D object pointed to by v, or a null pointer value if v is a null pointer value.

Similarly, if T is “reference to cv1 B” and v has type cv2 D such that B is a base class of D, the result is the unique B subobject of the D object referred to by v.47

In both the pointer and reference cases, the program is ill-formed if B is an inaccessible or ambiguous base class of D.

If v is a null pointer value, the result is a null pointer value.

If v has type “pointer to cv U” and v does not point to an object whose type is similar ([conv.qual]) to U and that is within its lifetime or within its period of construction or destruction ([class.cdtor]), the behavior is undefined.

If v is a glvalue of type U and v does not refer to an object whose type is similar to U and that is within its lifetime or within its period of construction or destruction, the behavior is undefined.

If T is “pointer to cv void”, then the result is a pointer to the most derived object pointed to by v.

Otherwise, a runtime check is applied to see if the object pointed or referred to by v can be converted to the type pointed or referred to by T.

Let C be the class type to which T points or refers.

The result of a typeid expression is an lvalue of static type const std​::​type_info ([type.info]) and dynamic type const std​::​type_info or const name where name is an implementation-defined class publicly derived from std​::​type_info which preserves the behavior described in [type.info].48

The lifetime of the object referred to by the lvalue extends to the end of the program.

Whether or not the destructor is called for the std​::​type_info object at the end of the program is unspecified.

If the type of the expression or type-id operand is a (possibly cv-qualified) class type or a reference to (possibly cv-qualified) class type, that class shall be completely defined.

If an expression operand of typeid is a possibly-parenthesized unary-expression whose unary-operator is * and whose operand evaluates to a null pointer value ([basic.compound]), the typeid expression throws an exception ([except.throw]) of a type that would match a handler of type std​::​bad_typeid ([bad.typeid]).

When typeid is applied to a glvalue whose type is a polymorphic class type ([class.virtual]), the result refers to a std​::​type_info object representing the type of the most derived object ([intro.object]) (that is, the dynamic type) to which the glvalue refers.

When typeid is applied to an expression other than a glvalue of a polymorphic class type, the result refers to a std​::​type_info object representing the static type of the expression.

When typeid is applied to a type-id, the result refers to a std​::​type_info object representing the type of the type-id.

If the type of the type-id is a reference to a possibly cv-qualified type, the result of the typeid expression refers to a std​::​type_info object representing the cv-unqualified referenced type.

If the type of the expression or type-id is a cv-qualified type, the result of the typeid expression refers to a std​::​type_info object representing the cv-unqualified type.

[Note 3:

Subclause [class.cdtor] describes the behavior of typeid applied to an object under construction or destruction.

— end note]

The result of the expression static_cast<T>(v) is the result of converting the expression v to type T.

If T is an lvalue reference type or an rvalue reference to function type, the result is an lvalue; if T is an rvalue reference to object type, the result is an xvalue; otherwise, the result is a prvalue.

An lvalue of type “cv1 B”, where B is a class type, can be cast to type “reference to cv2 D”, where D is a complete class derived ([class.derived]) from B, if cv2 is the same cv-qualification as, or greater cv-qualification than, cv1.

If B is a virtual base class of D or a base class of a virtual base class of D, or if no valid standard conversion from “pointer to D” to “pointer to B” exists ([conv.ptr]), the program is ill-formed.

An xvalue of type “cv1 B” can be cast to type “rvalue reference to cv2 D” with the same constraints as for an lvalue of type “cv1 B”.

If the object of type “cv1 B” is actually a base class subobject of an object of type D, the result refers to the enclosing object of type D.

Otherwise, the behavior is undefined.

An lvalue of type T1 can be cast to type “rvalue reference to T2” if T2 is reference-compatible with T1 ([dcl.init.ref]).

If the value is not a bit-field, the result refers to the object or the specified base class subobject thereof; otherwise, the lvalue-to-rvalue conversion is applied to the bit-field and the resulting prvalue is used as the operand of the static_cast for the remainder of this subclause.

If T2 is an inaccessible ([class.access]) or ambiguous ([class.member.lookup]) base class of T1, a program that necessitates such a cast is ill-formed.

Any expression can be explicitly converted to type cv void, in which case the operand is a discarded-value expression ([expr.prop]).

Otherwise, an expression E can be explicitly converted to a type T if there is an implicit conversion sequence ([over.best.ics]) from E to T, if overload resolution for a direct-initialization ([dcl.init]) of an object or reference of type T from E would find at least one viable function ([over.match.viable]), or if T is an aggregate type ([dcl.init.aggr]) having a first element x and there is an implicit conversion sequence from E to the type of x.

If T is a reference type, the effect is the same as performing the declaration and initialization T t(E); for some invented temporary variable t ([dcl.init]) and then using the temporary variable as the result of the conversion.

Otherwise, the result object is direct-initialized from E.

Otherwise, the lvalue-to-rvalue ([conv.lval]), array-to-pointer ([conv.array]), and function-to-pointer ([conv.func]) conversions are applied to the operand, and the conversions that can be performed using static_cast are listed below.

No other conversion can be performed using static_cast.

A value of a scoped enumeration type ([dcl.enum]) can be explicitly converted to an integral type; the result is the same as that of converting to the enumeration's underlying type and then to the destination type.

A value of a scoped enumeration type can also be explicitly converted to a floating-point type; the result is the same as that of converting from the original value to the floating-point type.

A value of integral or enumeration type can be explicitly converted to a complete enumeration type.

If the enumeration type has a fixed underlying type, the value is first converted to that type by integral promotion ([conv.prom]) or integral conversion ([conv.integral]), if necessary, and then to the enumeration type.

If the enumeration type does not have a fixed underlying type, the value is unchanged if the original value is within the range of the enumeration values ([dcl.enum]), and otherwise, the behavior is undefined.

A value of floating-point type can also be explicitly converted to an enumeration type.

The resulting value is the same as converting the original value to the underlying type of the enumeration ([conv.fpint]), and subsequently to the enumeration type.

A prvalue of floating-point type can be explicitly converted to any other floating-point type.

If the source value can be exactly represented in the destination type, the result of the conversion has that exact representation.

If the source value is between two adjacent destination values, the result of the conversion is an implementation-defined choice of either of those values.

Otherwise, the behavior is undefined.

A prvalue of type “pointer to cv1 B”, where B is a class type, can be converted to a prvalue of type “pointer to cv2 D”, where D is a complete class derived from B, if cv2 is the same cv-qualification as, or greater cv-qualification than, cv1.

If B is a virtual base class of D or a base class of a virtual base class of D, or if no valid standard conversion from “pointer to D” to “pointer to B” exists ([conv.ptr]), the program is ill-formed.

The null pointer value ([basic.compound]) is converted to the null pointer value of the destination type.

If the prvalue of type “pointer to cv1 B” points to a B that is actually a base class subobject of an object of type D, the resulting pointer points to the enclosing object of type D.

Otherwise, the behavior is undefined.

A prvalue of type “pointer to member of D of type cv1 T” can be converted to a prvalue of type “pointer to member of B of type cv2 T”, where D is a complete class type and B is a base class of D, if cv2 is the same cv-qualification as, or greater cv-qualification than, cv1.

If no valid standard conversion from “pointer to member of B of type T” to “pointer to member of D of type T” exists ([conv.mem]), the program is ill-formed.

If class B contains the original member, or is a base class of the class containing the original member, the resulting pointer to member points to the original member.

Otherwise, the behavior is undefined.

A prvalue of type “pointer to cv1 void” can be converted to a prvalue of type “pointer to cv2 T”, where T is an object type and cv2 is the same cv-qualification as, or greater cv-qualification than, cv1.

If the original pointer value represents the address A of a byte in memory and A does not satisfy the alignment requirement of T, then the resulting pointer value ([basic.compound]) is unspecified.

Otherwise, if the original pointer value points to an object a, and there is an object b of type similar to T that is pointer-interconvertible with a, the result is a pointer to b.

Otherwise, the pointer value is unchanged by the conversion.

The result of the expression reinterpret_cast<T>(v) is the result of converting the expression v to type T.

If T is an lvalue reference type or an rvalue reference to function type, the result is an lvalue; if T is an rvalue reference to object type, the result is an xvalue; otherwise, the result is a prvalue and the lvalue-to-rvalue, array-to-pointer, and function-to-pointer standard conversions are performed on the expression v.

Conversions that can be performed explicitly using reinterpret_cast are listed below.

No other conversion can be performed explicitly using reinterpret_cast.

The reinterpret_cast operator shall not cast away constness ([expr.const.cast]).

An expression of integral, enumeration, pointer, or pointer-to-member type can be explicitly converted to its own type; such a cast yields the value of its operand.

[Note 1:

The mapping performed by reinterpret_cast might, or might not, produce a representation different from the original value.

— end note]

A pointer can be explicitly converted to any integral type large enough to hold all values of its type.

The mapping function is implementation-defined.

A value of type std​::​nullptr_t can be converted to an integral type; the conversion has the same meaning and validity as a conversion of (void*)0 to the integral type.

A value of integral type or enumeration type can be explicitly converted to a pointer.

A pointer converted to an integer of sufficient size (if any such exists on the implementation) and back to the same pointer type will have its original value ([basic.compound]); mappings between pointers and integers are otherwise implementation-defined.

A function pointer can be explicitly converted to a function pointer of a different type.

The function pointer value is unchanged by the conversion.

An object pointer can be explicitly converted to an object pointer of a different type.49

When a prvalue v of object pointer type is converted to the object pointer type “pointer to cv T”, the result is static_cast<cv T*>(static_cast<cv void*>(v)).

Converting a function pointer to an object pointer type or vice versa is conditionally-supported.

The meaning of such a conversion is implementation-defined, except that if an implementation supports conversions in both directions, converting a prvalue of one type to the other type and back, possibly with different cv-qualification, shall yield the original pointer value.

The null pointer value ([basic.compound]) is converted to the null pointer value of the destination type.

A prvalue of type “pointer to member of X of type T1” can be explicitly converted to a prvalue of a different type “pointer to member of Y of type T2” if T1 and T2 are both function types or both object types.50

The null member pointer value ([conv.mem]) is converted to the null member pointer value of the destination type.

If v is a glvalue of type T1, designating an object or function x, it can be cast to the type “reference to T2” if an expression of type “pointer to T1” can be explicitly converted to the type “pointer to T2” using a reinterpret_cast.

The result is that of *reinterpret_cast<T2 *>(p) where p is a pointer to x of type “pointer to T1”.

The result of the expression const_cast<T>(v) is of type T.

If T is an lvalue reference to object type, the result is an lvalue; if T is an rvalue reference to object type, the result is an xvalue; otherwise, the result is a prvalue and the lvalue-to-rvalue, array-to-pointer, and function-to-pointer standard conversions are performed on the expression v.

Conversions that can be performed explicitly using const_cast are listed below.

No other conversion shall be performed explicitly using const_cast.

[Note 1:

Subject to the restrictions in this subclause, an expression can be cast to its own type using a const_cast operator.

— end note]

For two similar object pointer or pointer to data member types T1 and T2 ([conv.qual]), a prvalue of type T1 can be explicitly converted to the type T2 using a const_cast if, considering the qualification-decompositions of both types, each is the same as for all i.

If v is a null pointer or null member pointer, the result is a null pointer or null member pointer, respectively.

Otherwise, the result points to or past the end of the same object, or points to the same member, respectively, as v.

[Note 2:

Depending on the type of the object, a write operation through the pointer, lvalue or pointer to data member resulting from a const_cast that casts away a const-qualifier52 can produce undefined behavior ([dcl.type.cv]).

— end note]

A conversion from a type T1 to a type T2 casts away constness if T1 and T2 are different, there is a qualification-decomposition ([conv.qual]) of T1 yielding n such that T2 has a qualification-decomposition of the form ⋯ , and there is no qualification conversion that converts T1 to ⋯ .

Casting from an lvalue of type T1 to an lvalue of type T2 using an lvalue reference cast or casting from an expression of type T1 to an xvalue of type T2 using an rvalue reference cast casts away constness if a cast from a prvalue of type “pointer to T1” to the type “pointer to T2” casts away constness.

[Note 3:

Some conversions which involve only changes in cv-qualification cannot be done using const_cast.

For instance, conversions between pointers to functions are not covered because such conversions lead to values whose use causes undefined behavior.

For the same reasons, conversions between pointers to member functions, and in particular, the conversion from a pointer to a const member function to a pointer to a non-const member function, are not covered.

— end note]

The unary * operator performs indirection.

Its operand shall be a prvalue of type “pointer to T”, where T is an object or function type.

The operator yields an lvalue of type T.

If the operand points to an object or function, the result denotes that object or function; otherwise, the behavior is undefined except as specified in [expr.typeid].

Each of the following unary operators yields a prvalue.

The operand of the unary & operator shall be an lvalue of some type T.

• If the operand is a qualified-id or splice-expression designating a non-static member m, other than an explicit object member function, m shall be a direct member of some class C that is not an anonymous union.

  The result has type “pointer to member of class C of type T” and designates C​::​m.

  [Note 3:

  A qualified-id that names a member of a namespace-scope anonymous union is considered to be a class member access expression ([expr.prim.id.general]) and cannot be used to form a pointer to member.

  — end note]

• Otherwise, the result has type “pointer to T” and points to the designated object ([intro.memory]) or function ([basic.compound]).

  [Note 4:

  In particular, taking the address of a variable of type “cv T” yields a pointer of type “pointer to cv T”.

  — end note]

A pointer to member is only formed when an explicit & is used and its operand is a qualified-id or splice-expression not enclosed in parentheses.

If & is applied to an lvalue of incomplete class type and the complete type declares operator&(), it is unspecified whether the operator has the built-in meaning or the operator function is called.

The operand of & shall not be a bit-field.

[Note 7:

The address of an overload set ([over]) can be taken only in a context that uniquely determines which function is referred to (see [over.over]).

Since the context can affect whether the operand is a static or non-static member function, the context can also affect whether the expression has type “pointer to function” or “pointer to member function”.

— end note]

The operand of the unary + operator shall be a prvalue of arithmetic, unscoped enumeration, or pointer type and the result is the value of the argument.

Integral promotion is performed on integral or enumeration operands.

The type of the result is the type of the promoted operand.

The operand of the unary - operator shall be a prvalue of arithmetic or unscoped enumeration type and the result is the negative of its operand.

Integral promotion is performed on integral or enumeration operands.

The negative of an unsigned quantity is computed by subtracting its value from , where n is the number of bits in the promoted operand.

The type of the result is the type of the promoted operand.

The operand of the logical negation operator ! is contextually converted to bool ([conv]); its value is true if the converted operand is false and false otherwise.

The type of the result is bool.

The operand of the ~ operator shall be a prvalue of integral or unscoped enumeration type.

Integral promotions are performed.

The type of the result is the type of the promoted operand.

Given the coefficients of the base-2 representation ([basic.fundamental]) of the promoted operand x, the coefficient of the base-2 representation of the result r is 1 if is 0, and 0 otherwise.

The ambiguity is resolved by treating ~ as the operator rather than as the start of an unqualified-id naming a destructor.

The operand of prefix ++ or -- shall not be of type cv bool.

The expression ++x is otherwise equivalent to x+=1 and the expression --x is otherwise equivalent to x-=1 ([expr.assign]).

The co_await expression is used to suspend evaluation of a coroutine ([dcl.fct.def.coroutine]) while awaiting completion of the computation represented by the operand expression.

Suspending the evaluation of a coroutine transfers control to its caller or resumer.

An await-expression shall not appear in the initializer of a block variable with static or thread storage duration.

An await-expression shall not be a potentially-evaluated subexpression of the predicate of a contract assertion ([basic.contract]).

A context within a function where an await-expression can appear is called a suspension context of the function.

Evaluation of an await-expression involves the following auxiliary types, expressions, and objects:

• p is an lvalue naming the promise object ([dcl.fct.def.coroutine]) of the enclosing coroutine and P is the type of that object.

• Unless the await-expression was implicitly produced by a yield-expression ([expr.yield]), an initial await expression, or a final await expression ([dcl.fct.def.coroutine]), a search is performed for the name await_transform in the scope of P ([class.member.lookup]).

  If this search is performed and finds at least one declaration, then a is p.await_transform(cast-expression); otherwise, a is the cast-expression.

• o is determined by enumerating the applicable operator co_await functions for an argument a ([over.match.oper]), and choosing the best one through overload resolution ([over.match]).

  If overload resolution is ambiguous, the program is ill-formed.

  If no viable functions are found, o is a.

  Otherwise, o is a call to the selected function with the argument a.

  If o would be a prvalue, the temporary materialization conversion ([conv.rval]) is applied.

• e is an lvalue referring to the result of evaluating the (possibly-converted) o.

• h is an object of type std​::​coroutine_handle<P> referring to the enclosing coroutine.

• await-ready is the expression e.await_ready(), contextually converted to bool.

• await-suspend is the expression e.await_suspend(h), which shall be a prvalue of type void, bool, or std​::​coroutine_handle<Z> for some type Z.

• await-resume is the expression e.await_resume().

The await-expression has the same type and value category as the await-resume expression.

The await-expression evaluates the (possibly-converted) o expression and the await-ready expression, then:

• If the result of await-ready is false, the coroutine is considered suspended.

  Then:

  • If the type of await-suspend is std​::​coroutine_handle<Z>, await-suspend.resume() is evaluated.

    [Note 1:

    This resumes the coroutine referred to by the result of await-suspend.

    Any number of coroutines can be successively resumed in this fashion, eventually returning control flow to the current coroutine caller or resumer ([dcl.fct.def.coroutine]).

    — end note]

  • Otherwise, if the type of await-suspend is bool, await-suspend is evaluated, and the coroutine is resumed if the result is false.

  • Otherwise, await-suspend is evaluated.

  If the evaluation of await-suspend exits via an exception, the exception is caught, the coroutine is resumed, and the exception is immediately rethrown ([except.throw]).

  Otherwise, control flow returns to the current coroutine caller or resumer ([dcl.fct.def.coroutine]) without exiting any scopes ([stmt.jump]).

  The point in the coroutine immediately prior to control returning to its caller or resumer is a coroutine suspend point.

• If the result of await-ready is true, or when the coroutine is resumed other than by rethrowing an exception from await-suspend, the await-resume expression is evaluated, and its result is the result of the await-expression.

[Example 1: template <typename T> struct my_future { bool await_ready(); void await_suspend(std::coroutine_handle<>); T await_resume(); }; template <class Rep, class Period> auto operator co_await(std::chrono::duration<Rep, Period> d) { struct awaiter { std::chrono::system_clock::duration duration; awaiter(std::chrono::system_clock::duration d) : duration(d) {} bool await_ready() const { return duration.count() <= 0; } void await_resume() {} void await_suspend(std::coroutine_handle<> h) { } }; return awaiter{d}; } using namespace std::chrono; my_future<int> h(); my_future<void> g() { std::cout << "just about to go to sleep...\n"; co_await 10ms; std::cout << "resumed\n"; co_await h(); } auto f(int x = co_await h()); int a[] = { co_await h() }; — end example]

The sizeof operator yields the number of bytes occupied by a non-potentially-overlapping object of the type of its operand.

The sizeof operator shall not be applied to an expression that has function or incomplete type, to the parenthesized name of such types, or to a glvalue that designates a bit-field.

The result of sizeof applied to any of the narrow character types is 1.

The result of sizeof applied to any other fundamental type ([basic.fundamental]) is implementation-defined.

When applied to a reference type, the result is the size of the referenced type.

When applied to a class, the result is the number of bytes in an object of that class including any padding required for placing objects of that type in an array.

The result of applying sizeof to a potentially-overlapping subobject is the size of the type, not the size of the subobject.54

When applied to an array, the result is the total number of bytes in the array.

This implies that the size of an array of n elements is n times the size of an element.

The identifier in a sizeof... expression shall name a pack.

The sizeof... operator yields the number of elements in the pack ([temp.variadic]).

The result of sizeof and sizeof... is a prvalue of type std​::​size_t.

An alignof expression yields the alignment requirement of its operand type.

The operand shall be a type-id representing a complete object type, or an array thereof, or a reference to one of those types.

The result is a prvalue of type std​::​size_t.

When alignof is applied to a reference type, the result is the alignment of the referenced type.

When alignof is applied to an array type, the result is the alignment of the element type.

The operand of the noexcept operator is an unevaluated operand ([expr.context]).

If the operand is a prvalue, the temporary materialization conversion ([conv.rval]) is applied.

The result of the noexcept operator is a prvalue of type bool.

The result is false if the full-expression of the operand is potentially-throwing ([except.spec]), and true otherwise.

The new-expression attempts to create an object of the type-id or new-type-id ([dcl.name]) to which it is applied.

The type of that object is the allocated type.

[Example 1: new auto(1); auto x = new auto('a'); template<class T> struct A { A(T, T); }; auto y = new A{1, 2}; — end example]

The new-type-id in a new-expression is the longest possible sequence of new-declarators.

[Note 4:

Parentheses in a new-type-id of a new-expression can have surprising effects.

— end note]

Every constant-expression in a noptr-new-declarator shall be a converted constant expression ([expr.const]) of type std​::​size_t and its value shall be greater than zero.

[Note 6:

The lifetime of such an object is not necessarily restricted to the scope in which it is created.

— end note]

When the allocated type is “array of N T” (that is, the noptr-new-declarator syntax is used or the new-type-id or type-id denotes an array type), the new-expression yields a prvalue of type “pointer to T” that points to the initial element (if any) of the array.

Otherwise, let T be the allocated type; the new-expression is a prvalue of type “pointer to T” that points to the object created.

If the new-expression terminates by throwing an exception, it may release storage by calling a deallocation function.

If the allocated type is a non-array type, the allocation function's name is operator new and the deallocation function's name is operator delete.

If the allocated type is an array type, the allocation function's name is operator new[] and the deallocation function's name is operator delete[].

If the new-expression does not begin with a unary ​::​ operator and the allocated type is a class type T or array thereof, a search is performed for the allocation function's name in the scope of T ([class.member.lookup]).

Otherwise, or if nothing is found, the allocation function's name is looked up by searching for it in the global scope.

When it does so, the storage is instead provided by the implementation or provided by extending the allocation of another new-expression.

During an evaluation of a constant expression, a call to a replaceable allocation function is always omitted ([expr.const]).

When a new-expression calls an allocation function and that allocation has not been extended, the new-expression passes the amount of space requested to the allocation function as the first argument of type std​::​size_t.

That argument shall be no less than the size of the object being created; it may be greater than the size of the object being created only if the object is an array and the allocation function is not a non-allocating form ([new.delete.placement]).

For arrays of char, unsigned char, and std​::​byte, the difference between the result of the new-expression and the address returned by the allocation function shall be an integral multiple of the strictest fundamental alignment requirement of any object type whose size is no greater than the size of the array being created.

When a new-expression calls an allocation function and that allocation has been extended, the size argument to the allocation call shall be no greater than the sum of the sizes for the omitted calls as specified above, plus the size for the extended call had it not been extended, plus any padding necessary to align the allocated objects within the allocated memory.

The new-placement syntax is used to supply additional arguments to an allocation function; such an expression is called a placement new-expression.

Overload resolution is performed on a function call created by assembling an argument list.

The first argument is the amount of space requested, and has type std​::​size_t.

If the type of the allocated object has new-extended alignment, the next argument is the type's alignment, and has type std​::​align_val_t.

If the new-placement syntax is used, the initializer-clauses in its expression-list are the succeeding arguments.

[Example 6:

• new T results in one of the following calls: operator new(sizeof(T)) operator new(sizeof(T), std::align_val_t(alignof(T)))
• new(2,f) T results in one of the following calls: operator new(sizeof(T), 2, f) operator new(sizeof(T), std::align_val_t(alignof(T)), 2, f)
• new T[5] results in one of the following calls: operator new[](sizeof(T) * 5 + x) operator new[](sizeof(T) * 5 + x, std::align_val_t(alignof(T)))
• new(2,f) T[5] results in one of the following calls: operator new[](sizeof(T) * 5 + x, 2, f) operator new[](sizeof(T) * 5 + x, std::align_val_t(alignof(T)), 2, f)

Here, each instance of x is a non-negative unspecified value representing array allocation overhead; the result of the new-expression will be offset by this amount from the value returned by operator new[].

This overhead may be applied in all array new-expressions, including those referencing a placement allocation function, except when referencing the library function operator new[](std​::​size_t, void*).

The amount of overhead may vary from one invocation of new to another.

— end example]

If the allocation function is a non-allocating form ([new.delete.placement]) that returns null, the behavior is undefined.

Otherwise, if the allocation function returns null, initialization shall not be done, the deallocation function shall not be called, and the value of the new-expression shall be null.

[Note 11:

When the allocation function returns a value other than null, it must be a pointer to a block of storage in which space for the object has been reserved.

The block of storage is assumed to be appropriately aligned ([basic.align]) and of the requested size.

The address of the created object will not necessarily be the same as that of the block if the object is an array.

— end note]

A new-expression that creates an object of type T initializes that object as follows:

• If the new-initializer is omitted, the object is default-initialized ([dcl.init]).

  [Note 12:

  If no initialization is performed, the object has an indeterminate value.

  — end note]

• Otherwise, the new-initializer is interpreted according to the initialization rules of [dcl.init] for direct-initialization.

The invocation of the allocation function is sequenced before the evaluations of expressions in the new-initializer.

Initialization of the allocated object is sequenced before the value computation of the new-expression.

If the new-expression creates an array of objects of class type, the destructor is potentially invoked ([class.dtor]).

If any part of the object initialization described above56 terminates by throwing an exception and a suitable deallocation function can be found, the deallocation function is called to free the memory in which the object was being constructed, after which the exception continues to propagate in the context of the new-expression.

If no unambiguous matching deallocation function can be found, propagating the exception does not cause the object's memory to be freed.

If the new-expression does not begin with a unary ​::​ operator and the allocated type is a class type T or an array thereof, a search is performed for the deallocation function's name in the scope of T.

Otherwise, or if nothing is found, the deallocation function's name is looked up by searching for it in the global scope.

A declaration of a placement deallocation function matches the declaration of a placement allocation function if it has the same number of parameters and, after parameter transformations ([dcl.fct]), all parameter types except the first are identical.

If the lookup finds a single matching deallocation function, that function will be called; otherwise, no deallocation function will be called.

If the lookup finds a usual deallocation function and that function, considered as a placement deallocation function, would have been selected as a match for the allocation function, the program is ill-formed.

For a non-placement allocation function, the normal deallocation function lookup is used to find the matching deallocation function ([expr.delete]).

In any case, the matching deallocation function (if any) shall be non-deleted and accessible from the point where the new-expression appears.

If a new-expression calls a deallocation function, it passes the value returned from the allocation function call as the first argument of type void*.

If a placement deallocation function is called, it is passed the same additional arguments as were passed to the placement allocation function, that is, the same arguments as those specified with the new-placement syntax.

If the implementation is allowed to introduce a temporary object or make a copy of any argument as part of the call to the allocation function, it is unspecified whether the same object is used in the call to both the allocation and deallocation functions.

In a single-object delete expression, the value of the operand of delete may be a null pointer value, a pointer value that resulted from a previous non-array new-expression, or a pointer to a base class subobject of an object created by such a new-expression.

If not, the behavior is undefined.

In an array delete expression, the value of the operand of delete may be a null pointer value or a pointer value that resulted from a previous array new-expression whose allocation function was not a non-allocating form ([new.delete.placement]).58

If not, the behavior is undefined.

In a single-object delete expression, if the static type of the object to be deleted is not similar ([conv.qual]) to its dynamic type and the selected deallocation function (see below) is not a destroying operator delete, the static type shall be a base class of the dynamic type of the object to be deleted and the static type shall have a virtual destructor or the behavior is undefined.

In an array delete expression, if the dynamic type of the object to be deleted is not similar to its static type, the behavior is undefined.

If the object being deleted has incomplete class type at the point of deletion, the program is ill-formed.

If the value of the operand of the delete-expression is not a null pointer value and the selected deallocation function (see below) is not a destroying operator delete, evaluating the delete-expression invokes the destructor (if any) for the object or the elements of the array being deleted.

The destructor shall be accessible from the point where the delete-expression appears.

In the case of an array, the elements are destroyed in order of decreasing address (that is, in reverse order of the completion of their constructor; see [class.base.init]).

If the value of the operand of the delete-expression is a null pointer value, it is unspecified whether a deallocation function will be called as described above.

If a deallocation function is called, it is operator delete for a single-object delete expression or operator delete[] for an array delete expression.

Otherwise, or if nothing is found, the deallocation function's name is looked up by searching for it in the global scope.

Unless the deallocation function is selected at the point of definition of the dynamic type's virtual destructor, the selected deallocation function shall be accessible from the point where the delete-expression appears.

For a single-object delete expression, the deleted object is the object A pointed to by the operand if the static type of A does not have a virtual destructor, and the most-derived object of A otherwise.

For an array delete expression, the deleted object is the array object.

When a delete-expression is executed, the selected deallocation function shall be called with the address of the deleted object in a single-object delete expression, or the address of the deleted object suitably adjusted for the array allocation overhead ([expr.new]) in an array delete expression, as its first argument.

If a destroying operator delete is used, an unspecified value is passed as the argument corresponding to the parameter of type std​::​destroying_delete_t.

If a deallocation function with a parameter of type std​::​align_val_t is used, the alignment of the type of the deleted object is passed as the corresponding argument.

If a deallocation function with a parameter of type std​::​size_t is used, the size of the deleted object in a single-object delete expression, or of the array plus allocation overhead in an array delete expression, is passed as the corresponding argument.

The unary ^^ operator, called the reflection operator, yields a prvalue of type std​::​meta​::​info ([basic.fundamental]).

A reflect-expression is parsed as the longest possible sequence of tokens that could syntactically form a reflect-expression.

An unparenthesized reflect-expression that represents a template shall not be followed by <.

A reflect-expression of the form ^^​::​ represents the global namespace.

If a reflect-expression R matches the form ^^reflection-name, it is interpreted as such; the identifier is looked up and the representation of R is determined as follows:

• [Example 2: struct A { struct S {}; }; struct B : A { using A::S; }; constexpr std::meta::info r1 = ^^B::S; struct C : virtual B { struct S {}; }; struct D : virtual B, C {}; D::S s; constexpr std::meta::info r2 = ^^D::S; — end example]

• Otherwise, if lookup finds a namespace alias ([namespace.alias]), R represents that namespace alias.

• Otherwise, if lookup finds a namespace ([basic.namespace]), R represents that namespace.

• Otherwise, if lookup finds a concept ([temp.concept]), R represents the denoted concept.

• Otherwise, if lookup finds a template ([temp.names]), the representation of R is determined as follows:

  • If lookup finds an injected-class-name ([class.pre]), then:

    • Otherwise, the injected-class-name shall be unambiguous when considered as a type-name and R represents the class template specialization so named.

  • Otherwise, if lookup finds an overload set, that overload set shall contain only declarations of a unique function template F; R represents F.

  • Otherwise, if lookup finds a class template, variable template, or alias template, R represents that template.

    [Note 2:

    Lookup never finds a partial or explicit specialization.

    — end note]

• Otherwise, if lookup finds a type alias A, R represents the underlying entity of A if A was introduced by the declaration of a template parameter; otherwise, R represents A.

• Otherwise, if lookup finds a class or an enumeration, R represents the denoted type.

• Otherwise, if lookup finds a class member of an anonymous union ([class.union.anon]), R represents that class member.

A reflect-expression R of the form ^^type-id represents an entity determined as follows:

• Otherwise, R represents the type denoted by the type-id.

The result of the expression (T) cast-expression is of type T.

The result is an lvalue if T is an lvalue reference type or an rvalue reference to function type and an xvalue if T is an rvalue reference to object type; otherwise the result is a prvalue.

An explicit type conversion can be expressed using functional notation ([expr.type.conv]), a type conversion operator (dynamic_cast, static_cast, reinterpret_cast, const_cast), or the cast notation.

Any type conversion not mentioned below and not explicitly defined by the user ([class.conv]) is ill-formed.

The operand of a cast using the cast notation can be a prvalue of type “pointer to incomplete class type”.

The destination type of a cast using the cast notation can be “pointer to incomplete class type”.

If both the operand and destination types are class types and one or both are incomplete, it is unspecified whether the static_cast or the reinterpret_cast interpretation is used, even if there is an inheritance relationship between the two classes.

The pointer-to-member operators ->* and .* group left-to-right.

The binary operator .* binds its second operand, which shall be a prvalue of type “pointer to member of T” to its first operand, which shall be a glvalue of class T or of a class of which T is an unambiguous and accessible base class.

The result is an object or a function of the type specified by the second operand.

The binary operator ->* binds its second operand, which shall be a prvalue of type “pointer to member of T” to its first operand, which shall be of type “pointer to U” where U is either T or a class of which T is an unambiguous and accessible base class.

The expression E1->*E2 is converted into the equivalent form (*(E1)).*E2.

Abbreviating pm-expression.*cast-expression as E1.*E2, E1 is called the object expression.

If the result of E1 is an object whose type is not similar to the type of E1, or whose most derived object does not contain the member to which E2 refers, the behavior is undefined.

The expression E1 is sequenced before the expression E2.

The restrictions on cv-qualification, and the manner in which the cv-qualifiers of the operands are combined to produce the cv-qualifiers of the result, are the same as the rules for E1.E2 given in [expr.ref].

If the result of .* or ->* is a function, then that result can be used only as the operand for the function call operator ().

In a .* expression whose object expression is an rvalue, the program is ill-formed if the second operand is a pointer to member function whose ref-qualifier is &, unless its cv-qualifier-seq is const.

In a .* expression whose object expression is an lvalue, the program is ill-formed if the second operand is a pointer to member function whose ref-qualifier is &&.

The result of a .* expression whose second operand is a pointer to a data member is an lvalue if the first operand is an lvalue and an xvalue otherwise.

The result of a .* expression whose second operand is a pointer to a member function is a prvalue.

The multiplicative operators *, /, and % group left-to-right.

The operands of * and / shall have arithmetic or unscoped enumeration type; the operands of % shall have integral or unscoped enumeration type.

The binary * operator indicates multiplication.

The binary / operator yields the quotient, and the binary % operator yields the remainder from the division of the first expression by the second.

If the second operand of / or % is zero, the behavior is undefined.

For integral operands, the / operator yields the algebraic quotient with any fractional part discarded;59 if the quotient a/b is representable in the type of the result, (a/b)*b + a%b is equal to a; otherwise, the behavior of both a/b and a%b is undefined.

For subtraction, one of the following shall hold:

• both operands have arithmetic type; or
• both operands are pointers to cv-qualified or cv-unqualified versions of the same completely-defined object type; or
• the left operand is a pointer to a completely-defined object type and the right operand has integral type.

The result of the binary + operator is the sum of the operands.

The result of the binary - operator is the difference resulting from the subtraction of the second operand from the first.

When an expression J that has integral type is added to or subtracted from an expression P of pointer type, the result has the type of P.

• If P evaluates to a null pointer value and J evaluates to 0, the result is a null pointer value.

• Otherwise, if P points to a (possibly-hypothetical) array element i of an array object x with n elements ([dcl.array]),60 the expressions P + J and J + P (where J has the value j) point to the (possibly-hypothetical) array element of x if and the expression P - J points to the (possibly-hypothetical) array element of x if .

• Otherwise, the behavior is undefined.

The result of subtracting two pointer expressions P and Q is a prvalue of type std​::​ptrdiff_t ([support.types.layout]).

• If P and Q both evaluate to null pointer values, the value is 0.

• Otherwise, if P and Q point to, respectively, array elements i and j of the same array object x, the expression P - Q has the value .

  [Note 2:

  If the value is not in the range of representable values of type std​::​ptrdiff_t, the behavior is undefined ([expr.pre]).

  — end note]

• Otherwise, the behavior is undefined.

For addition or subtraction, if the expressions P or Q have type “pointer to cv T”, where T and the array element type are not similar, the behavior is undefined.

The value of E1 << E2 is the unique value congruent to modulo , where N is the width of the type of the result.

The value of E1 >> E2 is , rounded towards negative infinity.

The expression E1 is sequenced before the expression E2.

The three-way comparison operator groups left-to-right.

The expression p <=> q is a prvalue indicating whether p is less than, equal to, greater than, or incomparable with q.

If one of the operands is of type bool and the other is not, the program is ill-formed.

If both operands have arithmetic types, or one operand has integral type and the other operand has unscoped enumeration type, the usual arithmetic conversions are applied to the operands.

If both operands have the same enumeration type E, the operator yields the result of converting the operands to the underlying type of E and applying <=> to the converted operands.

If at least one of the operands is of object pointer type and the other operand is of object pointer or array type, array-to-pointer conversions ([conv.array]), pointer conversions ([conv.ptr]), and qualification conversions are performed on both operands to bring them to their composite pointer type ([expr.type]).

After the conversions, the operands shall have the same type.

Otherwise, the program is ill-formed.

The three comparison category types ([cmp.categories]) (the types std​::​strong_ordering, std​::​weak_ordering, and std​::​partial_ordering) are not predefined; if a standard library declaration ([compare.syn], [std.modules]) of such a class type does not precede ([basic.lookup.general]) a use of that type — even an implicit use in which the type is not named (e.g., via the auto specifier ([dcl.spec.auto]) in a defaulted three-way comparison ([class.spaceship]) or use of the built-in operator) — the program is ill-formed.

The relational operators group left-to-right.

If one of the operands is a pointer, the array-to-pointer conversion ([conv.array]) is performed on the other operand.

The converted operands shall have arithmetic, enumeration, or pointer type.

The operators < (less than), > (greater than), <= (less than or equal to), and >= (greater than or equal to) all yield false or true.

The type of the result is bool.

The usual arithmetic conversions ([expr.arith.conv]) are performed on operands of arithmetic or enumeration type.

After conversions, the operands shall have the same type.

The result of comparing unequal pointers to objects61 is defined in terms of a partial order consistent with the following rules:

• If two pointers point to different elements of the same array, or to subobjects thereof, the pointer to the element with the higher subscript is required to compare greater.

• If two pointers point to different non-static data members of the same object, or to subobjects of such members, recursively, the pointer to the later declared member is required to compare greater provided neither member is a subobject of zero size and their class is not a union.

• Otherwise, neither pointer is required to compare greater than the other.

If two operands p and q compare equal ([expr.eq]), p<=q and p>=q both yield true and p<q and p>q both yield false.

Otherwise, if a pointer to object p compares greater than a pointer q, p>=q, p>q, q<=p, and q<p all yield true and p<=q, p<q, q>=p, and q>p all yield false.

Otherwise, the result of each of the operators is unspecified.

If both operands (after conversions) are of arithmetic or enumeration type, each of the operators shall yield true if the specified relationship is true and false if it is false.

The == (equal to) and the != (not equal to) operators group left-to-right.

The lvalue-to-rvalue ([conv.lval]) and function-to-pointer ([conv.func]) standard conversions are performed on the operands.

If one of the operands is a pointer or a null pointer constant ([conv.ptr]), the array-to-pointer conversion ([conv.array]) is performed on the other operand.

The converted operands shall have scalar type.

The operators == and != both yield true or false, i.e., a result of type bool.

In each case below, the operands shall have the same type after the specified conversions have been applied.

Comparing pointers is defined as follows:

• If one pointer represents the address of a complete object, and another pointer represents the address one past the last element of a different complete object,62 the result of the comparison is unspecified.

• Otherwise, the pointers compare unequal.

If at least one of the operands is a pointer to member, pointer-to-member conversions ([conv.mem]), function pointer conversions ([conv.fctptr]), and qualification conversions ([conv.qual]) are performed on both operands to bring them to their composite pointer type ([expr.type]).

Two operands of type std​::​nullptr_t or one operand of type std​::​nullptr_t and the other a null pointer constant compare equal.

If both operands are of type std​::​meta​::​info, they compare equal if both operands

• are null reflection values,
• represent values that are template-argument-equivalent ([temp.type]),
• represent the same object,
• represent the same entity,
• represent the same annotation ([dcl.attr.annotation]),
• represent the same direct base class relationship, or
• represent equal data member descriptions ([class.mem.general]),