用一級指標和二級指標做引數，在函式裡面free一個一級指標，函式內和函式外是的地址什麼？
主要是用倆個例子演示
例一

static int free_param(LDAPMessage **res)
{
/* free the search results */
    if (res != NULL)
    {printf("5 \n");
    printf("res = %p\n", res); //res = 0xbea7cc78
    printf("res1 = %p\n", *res); //res1 = 0x12110
        ldap_msgfree(*res);
        *res = NULL;
    }
    printf("res = %p\n", res); //res = 0xbea7cc78
    return SUCC;
}
。。。
printf("res1 = %p\n", res); //res1 = 0x12110
free_param(&res);
printf("res1 = %p\n", res); //res1 = (nil)
。。。
 

static int free_param(LDAPMessage *res)
{
/* free the search results */
    if (res != NULL)
    {printf("5 \n");
    printf("res = %p\n", res); //res = 0x12110
        ldap_msgfree(res);
        res = NULL;
    }
    printf("res = %p\n", res); //res = (nil)
    return SUCC;
}
。。。
printf("res1 = %p\n", res); //res1 = 0x12110
free_param(res);
printf("res1 = %p\n", res); //res1 = 0x12110
。。。
 

例二

static int free_param( BerElement *ptr)
{
    printf("ptr = %p\n", ptr); 
    if (ptr != NULL)
    {printf("4 \n");
        ber_free(ptr, 0);
        ptr = NULL;
    }
    printf("ptr = %p\n\n", ptr);
    return SUCC;

}
。。。
free_param(ptr);
printf("ptr1 = %p\n", ptr);
free_param(ptr);
printf("ptr1 = %p\n", ptr);
。。。
 

結果：

ptr = 0x1a8f0
4 
ptr = (nil)

ptr1 = 0x1a8f0
ptr = 0x1a8f0
4 
*** glibc detected *** ./demo: double free or corruption (fasttop): 0x0001a8f0 ***

static int free_param( BerElement **ptr)
{
    printf("*ptr = %p\n", *ptr); 
    printf("ptr = %p\n", ptr); 
    if (*ptr != NULL)
    {printf("4 \n");
        ber_free(*ptr, 0);
        ptr = NULL;
    }
    printf("*ptr = %p\n", *ptr); 
    printf("ptr = %p\n", ptr);
    return SUCC;
}
。。。
free_param(&ptr);
printf("ptr1 = %p\n", ptr);
free_param(&ptr);
printf("ptr1 = %p\n", ptr);
。。。

結果：

*ptr = 0x1a3c8
ptr = 0xbed8fc74
4 
*ptr = (nil)
ptr = 0xbed8fc74

ptr1 = (nil)
*ptr = (nil)
ptr = 0xbed8fc74
*ptr = (nil)
ptr = 0xbed8fc74
ptr1 = (nil)