9 Declarations [dcl.dcl]

9.2 Declarators [dcl.decl]

9.2.1 Type names [dcl.name]

To specify type conversions explicitly, and as an argument of sizeof, alignof, new, or typeid, the name of a type shall be specified.
This can be done with a type-id, which is syntactically a declaration for a variable or function of that type that omits the name of the entity.
type-id:
	type-specifier-seq abstract-declarator
defining-type-id:
	defining-type-specifier-seq abstract-declarator
abstract-declarator:
	ptr-abstract-declarator
	noptr-abstract-declarator parameters-and-qualifiers trailing-return-type
	abstract-pack-declarator
ptr-abstract-declarator:
	noptr-abstract-declarator
	ptr-operator ptr-abstract-declarator
noptr-abstract-declarator:
	noptr-abstract-declarator parameters-and-qualifiers
	noptr-abstract-declarator [ constant-expression ] attribute-specifier-seq
	( ptr-abstract-declarator )
abstract-pack-declarator:
	noptr-abstract-pack-declarator
	ptr-operator abstract-pack-declarator
noptr-abstract-pack-declarator:
	noptr-abstract-pack-declarator parameters-and-qualifiers
	noptr-abstract-pack-declarator [ constant-expression ] attribute-specifier-seq
	...
It is possible to identify uniquely the location in the abstract-declarator where the identifier would appear if the construction were a declarator in a declaration.
The named type is then the same as the type of the hypothetical identifier.
Example
:
int                 // int i
int *               // int *pi
int *[3]            // int *p[3]
int (*)[3]          // int (*p3i)[3]
int *()             // int *f()
int (*)(double)     // int (*pf)(double)
name respectively the types “int”, “pointer to int”, “array of 3 pointers to int”, “pointer to array of 3 int”, “function of (no parameters) returning pointer to int”, and “pointer to a function of (double) returning int.
— end example
 ]
A type can also be named (often more easily) by using a typedef ([dcl.typedef]).