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

Question

I came across this piece of code and completely got lost interpreting its meaning. ``` #include void (*signal(int sig, void (*func)(int)))(int); ``` What is a detailed explanation for the code at line 2? I know that `void` and `int` are types, the *func is a pointer for a function, and the brackets are for priority. But I still don't get the (*signal ...), the (int), and the whole thing combined together. The more detailed, the better. Probably I've known the meaning/effect of this declaration. But I had to make some more trials to help me understand what's going on, as below: ``` 1 #include 2 void (*signal)(int sig, void (*func)(int)); 3 void (*signal)(int); // then void (signal)(int) again. 4 //void (*signal(int sig, void (*func)(int)))(int); //break this line into two lines above 5 6 int main(){} ``` In the above code, I broke `void (*signal(int sig, void (*func)(int)))(int)` into two lines. For line 3, I tried both `void (*signal)(int)` and `void (signal)(int…

Accepted Answer

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`).

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

Solution

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