Question

I have following typedef declarations in c but confused how I read these declarations.

   typedef char  *pc;     /* pc is pointer to char                      */
   typedef pc     fpc();  /* fpc is function returning pointer to char  */
   typedef fpc   *pfpc;
   typedef pfpc   fpfpc();
   typedef fpfpc *pfpfpc;
   pfpfpc a[N];

Now for me first two statement is easy to read but really confused after that.

Is there any way to solve(read) such equations?

Answer 1

typedef char  *pc;     /* pc is pointer to char                      */
typedef pc     fpc();  /* fpc is function returning pointer to char  */

Good so far. Note that the last typedef can also be written as

typedef char *fpc();

Next,

typedef fpc   *pfpc;

declares pfpc as a pointer to fpc. Since we know that fpc is a function returning a pointer to char, then pfpc must be a pointer to a function returning pointer to char, or

typedef char *(*pfpc)()  

Next we have

typedef pfpc   fpfpc();

This time, fpfpc is a function returning pfpc. Since we know that pfpc is a pointer to a function returning pointer to char, fpfpc must be a function returning a pointer to a function returning pointer to char, or

typedef char *(*fpfpc())();

Next, we have

typedef fpfpc *pfpfpc;

which declares pfpfpc as a pointer to fpfpc. Since we know fpfpc is a function returning a pointer to a function returning pointer to char, pfpfpc must be a pointer to a function returning a pointer to a function returning a pointer to char, or

typedef char *(*(*pfpfpc)())();

Finally, we have an an N-element array of pfpfpc

pfpfpc a[N];

Since we know pfpfpc is a pointer to a function returning pointers to functions returning pointers to char, then a must be an N-element array of pointers to functions returning pointers to functions returning pointers to char:

char *(*(*a[N])())();

The main rule to remember for reading and writing hairy declarations is that [] and () have higher precedence than *, so

*a[]       -- is an array of pointer
(*a)[]     -- is a pointer to an array
*f()       -- is a function returning a pointer
(*f)()     -- is a pointer to a function

and the whole thing is broken down as

          a                -- a
          a[N]             -- is an N-element array
         *a[N]             -- of pointers
        (*a[N])()          -- to functions
       *(*a[N])()          -- returning pointer
      (*(*a[N])())()       -- to function
     *(*(*a[N])())()       -- returning pointer
char *(*(*a[N])())()       -- to char

Going the other way, we have

         pfpfpc              -- is a synonym for
       *  fpfpc              -- is a synonym for
       *   pfpc()            -- is a synonym for
       *(* fpc)()            -- is a synonym for
       *(*pc())()            -- is a synonym for
char *(*(* )())()

The last step isn’t terribly intuitive, I’ll admit.