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-declaratoropt
defining-type-id: defining-type-specifier-seq abstract-declaratoropt
abstract-declarator: ptr-abstract-declarator noptr-abstract-declaratoropt parameters-and-qualifiers trailing-return-type abstract-pack-declarator
ptr-abstract-declarator: noptr-abstract-declarator ptr-operator ptr-abstract-declaratoropt
noptr-abstract-declarator: noptr-abstract-declaratoropt parameters-and-qualifiers noptr-abstract-declaratoropt [ constant-expressionopt ] attribute-specifier-seqopt ( 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-expressionopt ] attribute-specifier-seqopt ...
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 ]