C++ Primer, Fifth Edition

2.5.1. Type Aliases

A type alias is a name that is a synonym for another type. Type aliases let us simplify complicated type definitions, making those types easier to use. Type aliases also let us emphasize the purpose for which a type is used.

We can define a type alias in one of two ways. Traditionally, we use a typedef:

typedef double wages;   // wages is a synonym for doubletypedef wages base, *p; // base is a synonym for double, p for double*

The keyword typedef may appear as part of the base type of a declaration (§ 2.3, p. 50). Declarations that include typedef define type aliases rather than variables. As in any other declaration, the declarators can include type modifiers that define compound types built from the base type of the definition. ...