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    <p>The general procedure: find the leftmost identifier and work your way out. Absent an explicit grouping with parentheses, postfix operators such as <code>()</code> and <code>[]</code> bind before unary operators like <code>*</code>; thus, the following are all true:</p> <pre><code>T *x[N] -- x is an N-element array of pointer to T T (*x)[N] -- x is a pointer to an N-element array of T T *f() -- f is a function returning a pointer to T T (*f)() -- f is a pointer to a function returning T </code></pre> <p>Applying these rules to the declaration, it breaks down as</p> <pre><code> signal -- signal signal( ) -- is a function signal( signo, ) -- with a parameter named signo signal(int signo, ) -- of type int signal(int signo, func ) -- and a parameter named func signal(int signo, *func ) -- of type pointer signal(int signo, (*func)( )) -- to a function signal(int signo, (*func)(int)) -- taking an int parameter signal(int signo, void (*func)(int)) -- and returning void *signal(int signo, void (*func)(int)) -- returning a pointer (*signal(int signo, void (*func)(int)))( ) -- to a function (*signal(int signo, void (*func)(int)))(int) -- taking an int parameter void (*signal(int signo, void (*func)(int)))(int); -- and returning void </code></pre> <p>In short, <code>signal</code> returns a pointer to a function returning <code>void</code>. <code>signal</code> takes two parameters: an integer and a pointer to another function returning <code>void</code>. </p> <p>You could use typedefs to make this easier to read (and the man page for <code>signal</code> on Ubuntu linux does just that); however, I think it's valuable to show the non-typedef'd version to demonstrate exactly how the syntax works. The typedef facility is wonderful, but you really need to understand how the underlying types work in order to use it effectively. </p> <p>The <code>signal</code> function sets up a signal handler; the second argument is the function that is to be executed if a signal is received. A pointer to the current signal handler (if any) is returned. </p> <p>For example, if you want your program to handle interrupt signals (such as from Ctrl-C):</p> <pre><code>static int g_interruptFlag = 0; void interruptHandler(int sig) { g_interruptFlag = 1; } int main(void) { ... /** * Install the interrupt handler, saving the previous interrupt handler */ void (*oldInterruptHandler)(int) = signal(SIGINT, interruptHandler); while (!g_interruptFlag) { // do something interesting until someone hits Ctrl-C } /** * Restore the previous interrupt handler (not necessary for this particular * example, but there may be cases where you want to swap out signal handlers * after handling a specific condition) */ signal(SIGINT, oldInterruptHandler); return 0; } </code></pre> <p><strong>EDIT</strong> I extended the example code for <code>signal</code> to something that's hopefully more illustrative. </p>
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    1. CO+1 for a wonderful answer !
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