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typedef                  Derived Data Type Specifier

    The typedef keyword is used to invent a synonym for a type. This is
    useful for two reasons: to give a type a name that is more meaningful
    than one of C's basic types, and to give a name to a complex type
    declaration (so you need not keep reading and writing that complex
    type).  The format of a typedef is:

            typedef type declarator [[, declarator] ... ] ;

      Notes:    Many people don't use typedef--they use #define instead,
                since it can achieve the same result. However, there are
                many type declarations in which #define cannot be used in
                place of typedef. The point to remember is that typedef
                is part of the C language and it is processed by the
                compiler, which knows about types--typedef was
                specifically designed to give synonyms to types.
                #define, on the other hand, is part of the preprocessor,
                which knows nothing about C types--it merely provides a
                string substitution facility, and should be restricted to
                naming macros.

  -------------------------------- Example ---------------------------------

           typedef register fast;
           typedef char *string;
           typedef struct {double real, imag;} complex;
           typedef struct link *FNODE();

           fast total;
           string name, state;
           complex value;
           FNODE getnode;

            /*  In this last example, it is not immediately obvious that
                getnode is a function, since that property is hidden in
                the typedef, which is typically placed in a header.
                Therefore, the synonym should probably be defined as:  */

           typedef struct link *NODE; NODE getnode();