The "Clockwise/Spiral Rule'' By David Anderson

There is a technique known as the  "Clockwise/Spiral Rule'' which enables any C programmer to parse any C declaration!

There are three simple steps to follow:

1. Starting with the unknown element, move in a spiral/clockwise direction; when encountering the following elements replace them with the corresponding english statements:
1. [X] or []: Array X size of... or Array undefined size of...
2. (type1, type2): function passing type1 and type2 returning...
3. *: pointer(s) to...
2. Keep doing this in a spiral/clockwise direction until all tokens have been covered.
3. Always resolve anything in parenthesis first!

Example #1: Simple declaration

1. What is str? "str is an...
2. We move in a spiral clockwise direction starting with 'str' and the first character we see is a '[' so, that means we have an array, so..."str is an array 10 of...
3. Continue in a spiral clockwise direction, and the next thing we encounter is the '*' so, that means we have pointers, so..."str is an array 10 of pointers to...
4. Continue in a spiral direction and we see the end of the line (the ';'), so keep going and we get to the type 'char', so..."str is an array 10 of pointers to char''
5. We have now "visited'' every token; therefore we are done!

Example #2: Pointer to Function declaration

1. What is fp? "fp is a...
2. Moving in a spiral clockwise direction, the first thing we see is a `)'; therefore, fp is inside parenthesis, so we continue the spiral inside the parenthesis and the next character seen is the `*', so..."fp is a pointer to...
3. We are now out of the parenthesis and continuing in a spiral clockwise direction, we see the '('; therefore, we have a function, so..."fp is a pointer to a function passing an int and a pointer to float returning...
4. Continuing in a spiral fashion, we then see the '*' character, so..."fp is a pointer to a function passing an int and a pointer to float returning a pointer to...
5. Continuing in a spiral fashion we see the ';', but we haven't visited all tokens, so we continue and finally get to the type 'char', so..."fp is a pointer to a function passing an int and a pointer to float returning a pointer to a char"

Example #3: The "Ultimate"

1. What is 'signal'? Notice that signal is inside parenthesis, so we must resolve this first!
2. Moving in a clockwise direction we see '(' so we have..."signal is a function passing an int and a...
3. Hmmm, we can use this same rule on 'fp', so... What is fp? fp is also inside parenthesis so continuing we see an '*', so..."fp is a pointer to...
4. Continue in a spiral clockwise direction and we get to '(', so..."fp is a pointer to a function passing int returning...''
5. Now we continue out of the function parenthesis and we see void, so... "fp is a pointer to a function passing int returning nothing (void)''
6. We have finished with fp so let's catch up with 'signal', we now have... "signal is a function passing an int and a pointer to a function passing an int returning nothing (void) returning...
7. We are still inside parenthesis so the next character seen is a '*', so... "signal is a function passing an int and a pointer to a function passing an int returning nothing (void) returning a pointer to...
8. We have now resolved the items within parenthesis, so continuing clockwise, we then see another '(', so..."signal is a function passing an int and a pointer to a function passing an int returning nothing (void) returning a pointer to a function passing an int returning...
9. Finally we continue and the only thing left is the word 'void', so the final complete definition for signal is: "signal is a function passing an int and a pointer to a function passing an int returning nothing (void) returning a pointer to a function passing an int returning nothing (void)"