What’s the meaning of this piece of code? void (*signal(int sig, void (*func)(int)))(int);

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It’s the declaration of a function taking an int and a pointer to a function (taking int returning void) and returning a pointer to a function (taking int and returning void).

Explanation, or guide to interpretation

You can interpret by treating everything in parentheses as a single entity and then working inwards using the “declaration follows usage” rule.

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

The entity in the brackets looks like a function taking int and returning void.

Stripping away the outer part:

*signal(int sig, void (*func)(int))

So, signal takes some parameters and returns something that can be dereferenced (due to the leading *) to form a function taking int and returning void.

This means signal is a function returning a pointer to a function (taking int and returning void).

Looking at the parameters it takes an int (i.e. sig) and void (*func)(int) which is a pointer to a function (taking int and returning void).

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