9 Declarations [dcl.dcl]

9.2 Specifiers [dcl.spec]

9.2.9 Type specifiers [dcl.type] General [dcl.type.general]

The optional attribute-specifier-seq in a type-specifier-seq or a defining-type-specifier-seq appertains to the type denoted by the preceding type-specifiers or defining-type-specifiers ([dcl.meaning]).
The attribute-specifier-seq affects the type only for the declaration it appears in, not other declarations involving the same type.
As a general rule, at most one defining-type-specifier is allowed in the complete decl-specifier-seq of a declaration or in a defining-type-specifier-seq, and at most one type-specifier is allowed in a type-specifier-seq.
The only exceptions to this rule are the following:
  • const can be combined with any type specifier except itself.
  • volatile can be combined with any type specifier except itself.
  • signed or unsigned can be combined with char, long, short, or int.
  • short or long can be combined with int.
  • long can be combined with double.
  • long can be combined with long.
Except in a declaration of a constructor, destructor, or conversion function, at least one defining-type-specifier that is not a cv-qualifier shall appear in a complete type-specifier-seq or a complete decl-specifier-seq.78
[Note 1: 
enum-specifiers, class-specifiers, and typename-specifiers are discussed in [dcl.enum], [class], and [temp.res], respectively.
The remaining type-specifiers are discussed in the rest of [dcl.type].
— end note]
There is no special provision for a decl-specifier-seq that lacks a type-specifier or that has a type-specifier that only specifies cv-qualifiers.
The “implicit int” rule of C is no longer supported.