二級指標和一級指標
阿新 • • 發佈:2018-12-12
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)