Initializing structs in C++

Question

As an addendum to this question, what is going on here:

#include 
using namespace std;

struct A {
    string s;
};

int main() {
    A a = {0}         


        

Answer 1

As people have pointed out, this "works" because string has a constructor that can take 0 as a parameter. If we say:

#include 

then we get a compilation error, as the map class does not have such a constructor.