Difference between declaration of function with extern and without it

Question

There is such code:

#include <iostream>

extern void fun();

int main(){
    fun();
    return 0;
}

void fun(){ std::cout << "Hello" << std::endl; }

Is there some difference between declarations:

extern void fun();
void fun();

? Code above behaves the same with extern and without extern keyword.

Answer 1

Function declarations do have external linkage by default, so adding the extern keyword to a function declaration makes no difference, it is redundant.