C++补习 局部变量，引用，构造函数后冒号

class A
{
　　int a;
　　int b;

 public:  
    A( int aa, int bb ):a(aa),b(bb)
    {
    }
}

A( int aa, int bb )
{
a=aa;
b=bb;
}

#include <iostream>
using namespace std;
class A
{
public:
        A(int msg){
                this->msg = msg;
                cout<<"create A\n";
        }

        ~A(){
                cout<<"destroy A\n";
        }

        int msg;
};
void swap(A& a, A& b) {
        A temp = a;
        a = b;
        b = temp;
}

int main()
{
        A a(1);
        A b(2);

        std::cout<<"a="<<a.msg<<"b="<<b.msg;
        swap(a, b);
        std::cout<<"a="<<a.msg<<"b="<<b.msg;
        std::cout<<"hellow world";
        //a会被销毁吗？
        return 0;
}

void swap(A* a, A* b) {
        A* temp = a;
        a = b;
        b = temp;
}