7 Expressions [expr]

7.2 Properties of expressions [expr.prop]

7.2.2 Type [expr.type]

If an expression initially has the type “reference to T” ([dcl.ref], [dcl.init.ref]), the type is adjusted to T prior to any further analysis.
The expression designates the object or function denoted by the reference, and the expression is an lvalue or an xvalue, depending on the expression.
[Note
:
Before the lifetime of the reference has started or after it has ended, the behavior is undefined (see [basic.life]).
end note
]
If a prvalue initially has the type “cv T”, where T is a cv-unqualified non-class, non-array type, the type of the expression is adjusted to T prior to any further analysis.
The cv-combined type of two types T1 and T2 is a type T3 similar to T1 whose cv-qualification signature is:
  • for every , is the union of and ;
  • if the resulting is different from or , then const is added to every for .
[Note
:
Given similar types T1 and T2, this construction ensures that both can be converted to T3.
end note
]
The composite pointer type of two operands p1 and p2 having types T1 and T2, respectively, where at least one is a pointer or pointer-to-member type or std::nullptr_­t, is:
  • if both p1 and p2 are null pointer constants, std::nullptr_­t;
  • if either p1 or p2 is a null pointer constant, T2 or T1, respectively;
  • if T1 or T2 is “pointer to cv1 void” and the other type is “pointer to cv2 T”, where T is an object type or void, “pointer to cv12 void”, where cv12 is the union of cv1 and cv2;
  • if T1 or T2 is “pointer to noexcept function” and the other type is “pointer to function”, where the function types are otherwise the same, “pointer to function”;
  • if T1 is “pointer to cv1 C1” and T2 is “pointer to cv2 C2”, where C1 is reference-related to C2 or C2 is reference-related to C1, the cv-combined type of T1 and T2 or the cv-combined type of T2 and T1, respectively;
  • if T1 is “pointer to member of C1 of type cv1 U1” and T2 is “pointer to member of C2 of type cv2 U2” where C1 is reference-related to C2 or C2 is reference-related to C1, the cv-combined type of T2 and T1 or the cv-combined type of T1 and T2, respectively;
  • if T1 and T2 are similar types, the cv-combined type of T1 and T2;
  • otherwise, a program that necessitates the determination of a composite pointer type is ill-formed.
[Example
:
typedef void *p;
typedef const int *q;
typedef int **pi;
typedef const int **pci;
The composite pointer type of p and q is “pointer to const void”; the composite pointer type of pi and pci is “pointer to const pointer to const int.
end example
]