Can someone explain to me how 'sigaction' works?

I'm having difficulties understanding the way sigaction() works.

In <signal.h>, sigaction is defined as

int sigaction(int sig, const struct sigaction *act, struct sigaction *oact)

But sigaction is also defined in bits/si开发者_Python百科gaction.h as a structure. I'm confused here, can a struct in C be made callable?

Can someone please give me a brief explanation on this?

The function is called sigaction, the structure is called struct sigaction. Functions and structures exist in different namespaces in C. It is similar to the way you can do this:

#include <stdio.h>

struct x {
        int x;
};

static int
x(struct x *x) {
        return x->x;
}

int
main(void) {
        struct x y;
        /* But not "struct x x" as we want to call the "x" function below. */

        y.x = 1;
        printf("%d\n", x(&y));
        return 0;
}

And the compiler can sort out which x is which by the various namespaces. But this example is rather excessive and would get you some dirty looks if you did something like this in real life.