C syntax for functions returning function pointers

Question

Consider the following typedefs :

typedef int (*f1)(float); typedef f1 (*f2)(double); typedef f2 (*f3)(int); 

f2 is a function that returns a function pointer. The same with f3, but the type of the function, the pointer to which f3 returns, is f2. How can I define f3 without the typedefs? I know typedefs are the cleaner and easier to understand way to define f3. However, my intention here is to understand C syntax better.

Answer 1

Start with your declaration for f1:

int (*f1)(float); 

You want f2 to be a pointer to a function returning f1, so substitute f1 in the declaration above with the declaration for f2:

int (*      f1     )(float);             |       +-----+-----+       |           |       v           v int (*(*f2)(double))(float); 

The declaration reads as

        f2                   -- f2        *f2                   -- is a pointer       (*f2)(      )          -- to a function       (*f2)(double)          --   taking a double parameter      *(*f2)(double)          --   returning a pointer     (*(*f2)(double))(     )  --   to a function     (*(*f2)(double))(float)  --     taking a float parameter int (*(*f2)(double))(float)  --     returning int 

You repeat the process for f3:

int (*(*    f2    )(double))(float);             |         +---+----+         |        |         v        v int (*(*(*f3)(int))(double))(float); 

which reads as

          f3                           -- f3          *f3                           -- is a pointer         (*f3)(   )                     -- to a function         (*f3)(int)                     --   taking an int parameter        *(*f3)(int)                     --   returning a pointer       (*(*f3)(int))(      )            --   to a function       (*(*f3)(int))(double)            --     taking a double parameter      *(*(*f3)(int))(double)            --     returning a pointer     (*(*(*f3)(int))(double))(     )    --     to a function     (*(*(*f3)(int))(double))(float)    --       taking a float parameter int (*(*(*f3)(int))(double))(float);   --       returning int 

Answer 2

In C++, the miracle of templates can make this a tad easier.

#include <type_traits>  std::add_pointer<     std::add_pointer<         std::add_pointer<             int(float)         >::type(double)     >::type(int) >::type wow;