Complicated declarations (of C)

Question

Possible Duplicate:
How to understand complicated function declarations?
Spiral rule and ‘declaration follows usage’ for parsing C expressions

There is a section with the same title, "Complicated Declarations", in K&R's The C Programming Language book as you might have already read. I am just reading the book and trying to better myself in C language. After reading the section mentioned, I think I couldn't get the logic behind the syntax of C declaration statements. 1, 2, 3 and 4 are from that section 5 and 6 are from other pages.

1. int (*daytab)[13] daytab: pointer to array[13] of int

2. void (*comp)() comp: pointer to function returning void

3. char (*(*x())[])() x: function returning pointer to array[] of pointer to function returning char

4. char (*(*x[3])())[5] x: array[3] of pointer to function returning pointer to array[5] of char

5. typedef int (*PFI)(char *, char *) creates the type PFI, for ``pointer to function (of two char * arguments) returning int. How does the syntax works here?

Finally, my questions are:

• Can you explain your ways of thinking and reading complicated declarations possibly by using examples above?
• Are the things like 1,3,4 practically usable and needed? If so, can you write some code examples?

Answer 1

I saw The ``Clockwise/Spiral Rule'' on HackerNews in the past week or so. It is a good way to think about C declarations, especially function pointers.

Answer 2

Look at the identifier and the symbol next to it to the right:

• If it's a [ the identifier is for an array.
• If it is a ( the identifier is for a function
• If it is a ) look to the left and you will find a *: the identifier is a pointer
• If there is nothing to the right or to the left, the identifier is a "plain old" object.

Elaboration:

1. int (*daytab)[13]
daytab is a pointer

2. void (*comp)()
comp is a pointer

3. char (*(*x())[])()
x is a function

4. char (*(*x[3])())[5]
x is an array

5. typedef int (*PFI)(char *, char *)
PFI is a pointer