c - Function declaration inside of function — why?

Question

I am reading the book "Programming in C" and found in Chapter 10 an example like this:

#include <stdio.h>

void test (int??*int_pointer)
{
?????*int_pointer = 100;
}

int main (void)
{
?????void test (int??*int_pointer);
?????int??i = 50, *p = &i;

?????printf ("Before the call to test i = %i
", i);

?????test (p);
?????printf ("After the call to test i = %i
", i);

?????return 0;
}

I understand the example, but I don't understand the line void test (int *int_pointer); inside of main. Why do I define the signature of test again? Is that idiomatic C?

Answer 1

It's definitely not idiomatic C, despite being fully valid (multiple declarations are okay, multiple definitions are not). It's unnecessary, so the code will still work perfectly without it.

If at all, perhaps the author meant to do

void test (int *int_pointer);

int main (void) {

    ...

}

in case the function definition was put after main ().