Considerations for delete class object pointers]

http://blog.csdn.net/infoworld/article/details/45560219

Scene:
1. C + + classes have constructors and destructors that are used to release resources when class objects are deleted (or when local variables are automatically destroyed).

2. C + + Class object Pointers in many cases need to be assigned to void* universal pointers to achieve the purpose of transmitting objects, but often this void* pointer is the source of memory leaks or program errors,

This is why C + + has a generic purpose, and it is also designed to eliminate this object uncertainty at compile time, avoiding delete or use errors.

3. When you delete void* type, be careful to convert to class type only delete, such as delete (A *) Data_;

OK, look at the code, what's wrong with the following code?

[CPP]View Plaincopy

2. Test_class.cpp: Defines the entry point of the console application.
4. //
8. #include "stdafx.h"
10. #include <iostream>
14. Class A
16. {
18. Public
20. A ()
22. {
24. i = new int;
26. }
30. ~a ()
32. {
34. Delete I;
36. }
38. int* i;
40. };
44. Class B
46. {
48. Public
50. B (void* data)
52. {
54. Data_ = data;
56. }
60. ~b ()
62. {
64. Delete Data_;
66. }
68. void* Data_;
70. };
74. Template <class t>
76. Class C
78. {
80. Public
82. C (t* data)
84. {
86. Data_ = data;
88. }
90. ~c ()
92. {
94. Delete Data_;
96. }
100. t* Data_;
102. };
106. void Wrong ()
108. {
110. A *a = new A ();
112. b b (a); when the function returns, A's destructor does not call
114. }
118. void Right ()
120. {
122. A *a = new A ();
124. C<a> c (A); when the function returns, A's destructor is called
126. }
130. int _tmain (int argc, _tchar* argv[])
132. {
134. Wrong ();
136. Right ();
138. return 0;
140. }

Analytical:

B in the destructor Deleta Data_, looking at the disassembly code, and did not call the destructor.

[Plain]View Plaincopy

1. 011d1643 mov Eax,dword ptr [this]
2. 011d1646 mov ecx,dword ptr [eax]
3. 011d1648 mov dword ptr [EBP-0D4H],ECX
4. 011D164E mov edx,dword ptr [ebp-0d4h]
5. 011d1654 push edx
6. 011d1655 call operator Delete (11d1096h)

C in the destructor Deleta Data_, look at the disassembly code, there are call destructors.

[Plain]View Plaincopy

2. 011d1883 mov Eax,dword ptr [this]
4. 011d1886 mov ecx,dword ptr [eax]
6. 011d1888 mov dword ptr [EBP-0D4H],ECX
8. 011d188e mov edx,dword ptr [ebp-0d4h]
10. 011d1894 mov dword ptr [Ebp-0e0h],edx
12. 011D189A cmp DWORD ptr [ebp-0e0h],0
14. 011d18a1 JE c<a>::~c<a>+58h (11d18b8h)
16. 011D18A3 Push 1
18. 011D18A5 mov ecx,dword ptr [ebp-0e0h]
20. 011d18ab call A:: ' scalar deleting destructor ' (11D102DH)
22. 011D18B0 mov dword ptr [Ebp-0e8h],eax
24. 011d18b6 jmp c<a>::~c<a>+62h (11D18C2H)

Considerations for delete class object pointers]