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I am reading "The Linux Programming Interface", where I find signal system call prototype as stated:

#include <signal.h>
void ( *signal(int sig, void (*handler)(int)) ) (int);

What is signal here is it function-pointer or simple function?

I want to understand the reason behind putting last (int).

How come signal() is returning last desposition of SIGXXXX despite having void return type?

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The way to read

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

is that it declares a function, signal, which takes as arguments

  • an int
  • and a pointer to a function which itself takes an int and doesn’t return anything

and returns a pointer to a function which takes an int and doesn’t return anything.

The extra brackets correspond to the returned function pointer.

There’s a detailed explanation on Stack Overflow. Unfortunately cdecl.org doesn’t work on this declaration (because cdecl doesn’t either).

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