c++ void*類型轉換 delete void*

 

 1 #include <bits/stdc++.h>
 2 using namespace std;
 3 typedef long long LL;
 4 const int N=1e5+10;
 5 const int INF=0x3f3f3f3f;
 6 int cas=1,T;
 7 struct node{
 8     int *p;
 9     ~node()
10     {
11         cout<<"~node()\n";
12         if(p) delete p;
13     }
14 };
15 int main()
16 {
17     void * a=new float(3.0);
18     printf("%d %d\n",*((int*)a),(int)(*(float*)a));
19     delete a;
20     printf("%d %d\n",*((int*)a),(int)(*(float*)a));
21     a=new long long(3);
22     printf("%d %d\n",*((int*)a),(int)(*(long long*)a));
23     delete a;
24     printf("%d %d\n",*((int*)a),(int)(*(long long*)a));
25     node *b=new node;
26     b->p=new int(4);
27     int *c=b->p;
28     a=b;
29     delete a;
30     printf("p:%p\n",((node*)a)->p);
31     printf("%d\n",*c);
32     return 0;

test.cpp

 1 請按 ENTER 或其它命令繼續
 2 test.cpp: In function ‘int main()’:
 3 test.cpp:19:9: warning: deleting ‘void*’ is undefined [-Wdelete-incomplete]
 4   delete a;
 5          ^
 6 test.cpp:23:9: warning: deleting ‘void*’ is undefined [-Wdelete-incomplete]
 7   delete a;
 8          ^
 9 test.cpp:29:9: warning: deleting ‘void*’ is undefined [-Wdelete-incomplete]
10   delete a;
11          ^
12 
13 請按 ENTER 或其它命令繼續
14 1077936128 3
15 0 0
16 3 3
17 0 0
18 p:(nil)
19 4
20 
21 請按 ENTER 或其它命令繼續

result

 

void *a 原來的類型是float型，存的值是3.0,而後*((int*)a)直接強制將指針類型轉成int*以後輸出的值不是3,但(int)(*((float*)a))將a轉成float*以後再將值轉成(int)輸出的值就是3了，說明void*指針強制轉換後仍是會讀到原來的二進制，沒有進行指針所指向的值的轉換

delete a以後兩個值都爲0說明delete void能成功delete void*成功,後面的結構體沒有輸出~node()說明沒有調用自定義類型的~node()函數，只是將該指針指向的內存free調，也說明系統會記住一個指針所指向的內存的大小

後面的long long結果不變說明void*強制轉換時若是大小不同採用尾截法取指向的內存