How to understand this define

Question

Nowadays , i was reading the APUE.and i found the function defined as below:

void (*signal(int signo, void (*func)(int)))(int);

i was confused,

Answer 1

The Clockwise Spiral rule will help: http://c-faq.com/decl/spiral.anderson.html

There are three simple steps to follow:

Starting with the unknown element, move in a spiral/clockwise direction; when ecountering the following elements replace them with the corresponding english statements:

[X] or [] => Array X size of... or Array undefined size of...

(type1, type2) => function passing type1 and type2 returning...

• => pointer(s) to...

Keep doing this in a spiral/clockwise direction until all tokens have been covered. Always resolve anything in parenthesis first!

See "Example #3: The 'Ultimate'", which is pretty much exactly what you are asking for:

"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)"