void test(){
    int a = 10;
    //ra是一个引用,ra是a的别名
    int& ra = a;

    A sa;
    sa.a = 1;
    sa.b = 1;
    //引用不分配新的空间
    A& rsa = sa;
    //拷贝会分配新的空间
    A copy = sa;


    copy.a = 5;   //不会印象sa中的变量
    rsa.a = 10;   //会印象sa中的变量

}

 

void test1(){
    //引用必须初始化
    int a = 10;
    //变量有多个引用
    int& ra = a;
    int& ra1 = a;
    int& ra2 = a;
    //都可以改变a的值
    ra = 5;
    ra1 = 10;
    ra2 = 20;
    a = 30;

}

 

void test2(){
//常引用:引用指向的实体不能修改

    const int a = 10;
    const int& ra = a;
    
    double d = 2.5;
    int c = 10;
    c = d;
    const int& ra3 = d;

}

 

//交换函数
   //指针
void Swap(int* a, int* b){
    int tmp = *a;
    *a = *b;
    *b = tmp;
}
   //引用
void Swap(int& a, int& b){
    int tmp = a;
    a = b;
    b = tmp; 
}

 

//返回值引用
int& add(int& a, int& b){
    return a += b;
}
void test3(){
    int a = 10;
    int b = 20;
    int& ra = add(a, b);  //ra=30,a=30,b=20
}