3.18 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. For example, the following defines a new type called "eggbox" using an existing type called "egg":

         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 was 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, there is another (preferred) syntax that may be used to define the same type. In general, a typedef of the following form:

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

may be converted to the alternative form by removing the "typedef" part and placing the identifier after the "struct", "union", or "enum" 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
         };

The reason this syntax is preferred is one does not have to wait until the end of a declaration to figure out the name of the new type.