为什么在这段代码中有核心转储我看到了输出

Catch 
terminate called after throwing an instance of 'std::runtime_error'
  what():  ZERO DIV
Aborted (core dumped)

但我希望

Catch 
    terminate called after throwing an instance of 'std::runtime_error'
      what():  ZERO DIV

我的密码

class Q {
public:
    Q(int a, int b) try
    : val(b != 0 ? a / b : throw runtime_error("ZERO DIV"))
    {
        cout << "Q()" << endl;
    }
    catch(...)
    {
        cout << "Catch " << endl;
        val = nullopt;
    }
    ~Q() {
        cout << "~Q()" << endl;
    }
private:
    optional<int> val;
};

int main() {
    Q q = {1, 0};
    return 0;
}

我认为核心转储的原因是a / B的执行，但我不应该被执行，因为b不为零