Virtual table pointer

chllcy88

1. #include <iostream>
   
2. #include <iomanip>
   
3. using namespace std;
   
4. int nop() {
   
5.   static int nop_x; return ++nop_x; // Don't remove me, compiler!
   
6. };
   
7. 
   
8. class A
   
9. {
   
10. public:
    
11.   unsigned long long content_A;
    
12.   A(void) : content_A(0xAAAAAAAAAAAAAAAAull)
    
13.       { cout << "++ A has been constructed" << endl;};
    
14.   ~A(void)
    
15.       { cout << "-- A has been destructed" << endl;};
    
16. 
    
17.   void function(void) { nop(); };
    
18. };
    
19. 
    
20. void PrintMemory(const unsigned char memory[],
    
21.                  const char label[] = "contents")
    
22. {
    
23.   cout << "Memory " << label << ": " << endl;
    
24.   for (size_t i = 0; i < 4; i++)
    
25.   {
    
26.     for (size_t j = 0; j < 8; j++)
    
27.       cout << setw(2) << setfill('0') << uppercase << hex
    
28.            << static_cast<int> (memory[i * 8 + j]) << " ";
    
29.     cout << endl;
    
30.   }
    
31. }
    
32. 
    
33. int main()
    
34. {
    
35.   unsigned char memory[32];
    
36.   memset(memory, 0x11, 32 * sizeof(unsigned char));
    
37.   PrintMemory(memory, "before placement new");
    
38. 
    
39.   new (memory) A;
    
40.   PrintMemory(memory, "after placement new");
    
41.   reinterpret_cast<A *>(memory)->~A();
    
42. 
    
43.   system("pause");
    
44.   return 0;
    
45. };

复制代码

帮忙看下红色（39行new (memory) A;）这句该如何理解啊？原文http://www.cplusplus.com/articles/iy6AC542/

hellioncu

placement new，在memory位置创建A的实例