程序代码：

//bccn.cpp
#include <stdio.h>
#include <stdlib.h>
typedef struct
{
    int yyy;
}Snode;
void Empty_p(Snode *s)
{
    if (s)
    {
        free(s);
        printf (" \tfree...... \n");
        s = NULL;
    }
}
void Empty_ref(Snode *&s)
{
    if (s)
    {
        free(s);
        printf (" \tfree...... \n");
        s = NULL;
    }
}
int main()
{
    Snode *s = NULL;
    Snode *t = NULL;
    s = (Snode*) malloc(sizeof(Snode));
    t = (Snode*) malloc(sizeof(Snode));
    if (s)
    {
        printf ("s = %p\n", s);
        Empty_p(s);
        printf ("s = %p\n", s);
    }
    if (t)
    {
        printf ("t = %p\n", t);
        Empty_ref(t);
        printf ("t = %p\n", t);
    }
    return 0;
}