void &r=x; //不能建立void类型引用

int &&r=x; //不能建立引用的引用

int &*p=x; //不能建立指向引用的指针，但是可以建立指向指针的引用

int &ra[]=a; //不能建立引用的数组

#include<iostream>

using namespace std;

int x=,y=;

int &r=x;

void print()

{

    cout<<"x="<<x<<" y=<<y<<" r="<<endl;

    cout<<"Address of x "<<&x<<endl;

    cout<<"Address of y "<<&y<<endl;

    cout<<"Address of z "<<&z<<endl;

}

int main()

{

    print();

    r=y;

    y=;

    print();

    x=;

    print();

    return ;

}

运行结果如下：
x= y= r=

Address of x 00474DD0

Address of y 00474DD4

Address of r 00474DD0

x= y= r=

Address of x 00474DD0

Address of y 00474DD4

Address of r 00474DD0

x= y= r=

Address of x 00474DD0

Address of y 00474DD4

Address of r 00474DD0

 #include <iostream>

 using namespace std;

 void swap(int &x,int &y)

 {

     int t=x;

     x=y;

     y=t;

 }

 int main()

 {

     int a=,b=,c=,d=;

     cout<<"a="<<a<<" b="<<b<<endl;

     swap(a,b);

     cout<<"a="<<a<<" b="<<b<<endl;

     cout<<"c="<<c<<" d="<<d<<endl;

     swap(c,d);

     cout<<"c="<<c<<" d="<<d<<endl;

     return ;

 }