Question

Could someone explain what is going on when we use the typedef “type
cast” syntax?

    typedef int (*funcptr)(double); (Wiki)
    funcptr x = (funcptr) NULL;

OR

pg470, K.N.King – Modern Approach

    typedef int *Fcn(void);
    typedef Fcn *Fcn_ptr;
    typedef Fcn_ptr Fcn_ptr_array[10];
    Fcn_ptr_array x;

Isn’t it:

    typedef oldtype newtype;
    typedef int Bool;

So how does: typedef int * Fcn(void) make sense??
Usually: int *Fcn(void), would be a function “Fcn” that has no
parameters and returns a pointer to an int.. if i stick a typedef what
happens??

funcptr is a pointer variable.. it’s not a type..? so how can he cast
NULL to (funcptr)???? Is this syntax explained clearly somewhere –
K.N.King just slams it into you without mentioning this peculiar syntax
anywhere..

Answer 1

from 《C language reference manual》, chapter 7:

Declarations with the storage class specifier typedef do not define storage. A typedef has the following syntax: typedef-name: identifier.An identifier appearing in a typedef declaration becomes a synonym for the type rather than becoming an object with the given type.

so typedef int (*funcptr)(double) means funcptr is a function pointer,the function has one parameter double and return type is int.