What does this declaration typedef void foo(); mean? [closed]

Question

I don't understand the meaning of typedef void interrupt_handler();. Could someone explain it with some examples?

typedef void interrupt_handler();

Answer 1

It means that interrupt_handler is type synonym for function, that returns void and does not specify its parameters (so called old-style declaration). See following example, where foo_ptr is used as function pointer (this is special case where parentheses are not needed):

#include <stdio.h>

typedef void interrupt_handler();

void foo()
{
    printf("foo\n");
}

int main(void)
{
    void (*foo_ptr_ordinary)() = foo;
    interrupt_handler *foo_ptr = foo; // no need for parantheses

    foo_ptr_ordinary();
    foo_ptr();

    return 0;
}