C++動態空間的申請

為什麼C++的動態分配是new和delete？

因為malloc 函數和對應的free函數不能調用構造函數和析構函數，這破壞了空間分配、初始化的功能。所以引入了new和delete。

1. //============================================================================
2. // Name : main.cpp
3. // Author : ShiGuang
4. // Version :
5. // Copyright : [email protected]
6. // Description : Hello World in C++, Ansi-style
7. //============================================================================
9. #include <iostream>
10. #include <string>
11. using namespace std;
13. class aa
14. {
15. public:
16. aa(int a = 1)
17. {
18. cout << "aa is constructed." << endl;
19. id = a;
20. }
21. int id;
22. ~aa()
23. {
24. cout << "aa is completed." << endl;
25. }
26. };
28. int main(int argc, char **argv)
29. {
30. aa *p = new aa(9);
31. cout << p->id << endl;
32. delete p;
34. cout << "" << endl;
36. aa *q = (aa *) malloc(sizeof(aa));
37. cout << q->id << endl;//隨機數 表明構造函數未調用
38. free(q);//析構函數未調用
39. }

1. aa is constructed.
2. 9
3. aa is completed.
5. 3018824

堆空間不伴隨函數動態釋放，程序員要自主管理

1. //============================================================================
2. // Name : main.cpp
3. // Author : ShiGuang
4. // Version :
5. // Copyright : [email protected]
6. // Description : Hello World in C++, Ansi-style
7. //============================================================================
9. #include <iostream>
10. #include <string>
11. using namespace std;
13. class aa
14. {
15. public:
16. aa(int a = 1)
17. {
18. cout << "aa is constructed." << endl;
19. id = a;
20. }
21. ~aa()
22. {
23. cout << "aa is completed." << endl;
24. }
25. int id;
26. };
28. aa & m()
29. {
30. aa *p = new aa(9);
31. delete p;
32. return (*p);
33. }
35. int main(int argc, char **argv)
36. {
37. aa & s = m();
38. cout << s.id;// 結果為隨機數，表明被釋放
39. }