Typedef

Typedef does not declare any data either, but serves to define new identifiers for declaring data. The syntax is:

typedef declaration;

The new type name is actually the variable name in the declaration part of the typedef. The following example defines a new type called eggbox using an existing type called egg and the symbolic constant DOZEN.

typedef egg eggbox[DOZEN];

Variables declared using the new type name have the same type as the new type name would have in the typedef, if it were considered a variable. For example, the following two declarations are equivalent in declaring the variable fresheggs:

eggbox fresheggs;
 egg fresheggs[DOZEN];

When a typedef involves a struct, enum, or union definition, you can use another (preferred) syntax to define the same type. In general, a typedef of the following form:

typedef <<struct, union, or enum definition>> identifier;

can be converted to the alternative form by removing the typedef part and placing the identifier after the struct, enum, or union keyword instead of at the end. For example, here are the two ways to define the type bool.

typedef enum {/* using typedef */
   FALSE = 0,
   TRUE = 1
} bool;
enum bool {/* preferred alternative */
   FALSE = 0,
   TRUE = 1
};

This syntax is preferred because you do not have to go to the end of a declaration to learn the name of the new type.