c vs c++ in strcut and class

c vs c++ in strcut and class

总习惯用c的用法，现在学习C++，老爱拿来比较。声明我用的是g++4.2.1 SUSE Linux。看例子吧

1. #include <iostream>
2. #include <cstring>
3. #include <string>
4. using namespace std;
5. enum zoo_obj_kind{
6. null = 0,
7. #define null null
8. no = 0,
9. #define no no
10. animal = 2,
11. #define animal animal
12. plant = 4,
13. #define plant plant
14. others = 8
15. #define others others
16. };
17. struct zoo_obj{
18. zoo_obj_kind zo_kind;
19. char name [40];
20. };
21. class zoo_obj_1{
22. zoo_obj_kind zo_kind;
23. char name [40];
24. };
25. int main(void){
26. cout << "struct :" << sizeof(struct zoo_obj) << endl;
27. cout << "clsas :" << sizeof( zoo_obj_1) << endl;
28. }

结果

1. struct size:44
2. clsas size:44

-------------------------------

1. #include <iostream>
2. #include <cstring>
3. #include <string>
4. using namespace std;
5. enum zoo_obj_kind{
6. null = 0,
7. #define null null
8. no = 0,
9. #define no no
10. animal = 2,
11. #define animal animal
12. plant = 4,
13. #define plant plant
14. others = 8
15. #define others others
16. };
17. struct zoo_obj{
18. zoo_obj_kind zo_kind;
19. char name [40];
20. void (*say)(struct zoo_obj *);
21. };
22. void say(struct zoo_obj *obj){
23. if(!obj) {
24. printf("null\n");
25. return ;
26. }
27. printf("name:%s\n",obj->name);
28. }
29. class zoo_obj_1{
30. zoo_obj_kind zo_kind;
31. char name [40];
32. void say(zoo_obj_1 &obj){
33. cout << "name:" << name << endl;
34. }
35. };
36. int main(void){
37. cout << "struct :" << sizeof(struct zoo_obj) << endl;
38. cout << "clsas :" << sizeof( zoo_obj_1) << endl;
39. }

结果

1. struct size:48
2. clsas size:44

呵呵，有意思吧，在class中成员函数不占空间。下面你看看他们有多像

 

1. #include <iostream>
2. #include <cstring>
3. #include <string>
4. using namespace std;
5. enum zoo_obj_kind{
6. null = 0,
7. #define null null
8. no = 0,
9. #define no no
10. animal = 2,
11. #define animal animal
12. plant = 4,
13. #define plant plant
14. others = 8
15. #define others others
16. };
17. struct zoo_obj{
18. zoo_obj_kind zo_kind;
19. char name [40];
20. void (*say)(struct zoo_obj &);
21. };
22. void say(struct zoo_obj &obj){
23. printf("name:%s\n",obj.name);
24. }
25. class zoo_obj_1{
26. public:
27. zoo_obj_kind zo_kind;
28. char name [40];
29. void say(){cout << "name:" << name << endl;}
30. void say(zoo_obj_1 &obj){cout << "name:" << obj.name << endl;}
31. };
32. typedef struct zoo_obj s_zoo_obj;
33. typedef zoo_obj_1 c_zoo_obj;
34. int main(void){
35. s_zoo_obj s_obj = {animal,"dog",say};
36. zoo_obj_1 c_obj = {animal,"cat"};
37. cout << "struct size:" << sizeof(struct zoo_obj) << endl;
38. cout << "clsas size:" << sizeof( zoo_obj_1) << endl;
39. s_obj.say(s_obj);
40. c_obj.say(c_obj);
41. }

结果

1. struct size:48
2. clsas size:44
3. name:dog
4. name:cat

这是同时使用了引用，那么指针呢。struct的指针当然没有问题，那么class的指针呢？看看代码

1. #include <iostream>
2. #include <cstring>
3. #include <string>
4. using namespace std;
5. enum zoo_obj_kind{
6. null = 0,
7. #define null null
8. no = 0,
9. #define no no
10. animal = 2,
11. #define animal animal
12. plant = 4,
13. #define plant plant
14. others = 8
15. #define others others
16. };
17. struct zoo_obj{
18. zoo_obj_kind zo_kind;
19. char name [40];
20. void (*say)(struct zoo_obj *);
21. };
22. void say(struct zoo_obj *obj){
23. !obj
24. ? printf("null\n")
25. : printf("name:%s\n",obj->name);
26. }
27. class zoo_obj_1{
28. public:
29. zoo_obj_kind zo_kind;
30. char name [40];
31. void say(){cout << "name:" << name << endl;}
32. void say(zoo_obj_1 *obj){
33. !obj
34. ? cout << "null\n"
35. : cout << "name:" << obj->name << endl;
36. }
37. };
38. typedef struct zoo_obj s_zoo_obj;
39. typedef zoo_obj_1 c_zoo_obj;
40. int main(void){
41. s_zoo_obj s_obj = {animal,"dog",say};
42. zoo_obj_1 c_obj = {animal,"cat"};
43. cout << "struct size:" << sizeof(struct zoo_obj) << endl;
44. cout << "clsas size:" << sizeof( zoo_obj_1) << endl;
45. s_obj.say(&s_obj);
46. c_obj.say(&c_obj);
47. s_obj.say(NULL);
48. c_obj.say(NULL);
49. }

哈哈，结果仍然是

 

1. struct size:48
2. clsas size:44
3. name:dog
4. name:cat

更高级的特性呢？

比如在继承，接口。。。

个人认为C的这类名词没有，但他确实能出色的实现诸如此类的功能，而且更直观。可能是我的C++还不行吧。C高效和简单直观是没得说的。