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>
  5. using namespace std;
  7. enum zoo_obj_kind{
  8.         null = 0,
  9. #define null null
  10.         no = 0,
  11. #define no no
  12.         animal = 2,
  13. #define animal animal
  14.         plant = 4,
  15. #define plant plant
  16.         others = 8
  17. #define others others
  19. };
  21. struct zoo_obj{
  22.         zoo_obj_kind zo_kind;
  23.         char name [40];
  24. };
  25. class zoo_obj_1{
  26.         zoo_obj_kind zo_kind;
  27.         char name [40];
  29. };
  31. int main(void){
  33.         cout << "struct :" << sizeof(struct zoo_obj) << endl;
  34.         cout << "clsas :" << sizeof( zoo_obj_1) << endl;
  37. }
结果
  1. struct size:44
  2. clsas size:44
-------------------------------
  1. #include <iostream>
  2. #include <cstring>
  3. #include <string>
  5. using namespace std;
  7. enum zoo_obj_kind{
  8.         null = 0,
  9. #define null null
  10.         no = 0,
  11. #define no no
  12.         animal = 2,
  13. #define animal animal
  14.         plant = 4,
  15. #define plant plant
  16.         others = 8
  17. #define others others
  19. };
  21. struct zoo_obj{
  22.         zoo_obj_kind zo_kind;
  23.         char name [40];
  24.         void (*say)(struct zoo_obj *);
  25. };
  26. void say(struct zoo_obj *obj){
  27.         if(!obj) {
  28.                 printf("null ");
  29.                 return ;
  30.         }
  31.         printf("name:%s ",obj->name);
  33. }
  34. class zoo_obj_1{
  35.         zoo_obj_kind zo_kind;
  36.         char name [40];
  37.         void say(zoo_obj_1 &obj){
  38.                 cout << "name:" << name << endl;
  40.         }
  41. };
  43. int main(void){
  45.         cout << "struct :" << sizeof(struct zoo_obj) << endl;
  46.         cout << "clsas :" << sizeof( zoo_obj_1) << endl;
  49. }
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>
  5. using namespace std;
  7. enum zoo_obj_kind{
  8.         null = 0,
  9. #define null null
  10.         no = 0,
  11. #define no no
  12.         animal = 2,
  13. #define animal animal
  14.         plant = 4,
  15. #define plant plant
  16.         others = 8
  17. #define others others
  19. };
  21. struct zoo_obj{
  22.         zoo_obj_kind zo_kind;
  23.         char name [40];
  24.         void (*say)(struct zoo_obj &);
  25. };
  26. void say(struct zoo_obj &obj){
  27.         printf("name:%s ",obj.name);
  29. }
  30. class zoo_obj_1{
  31.         public:
  32.         zoo_obj_kind zo_kind;
  33.         char name [40];
  34.         void say(){cout << "name:" << name << endl;}
  35.         void say(zoo_obj_1 &obj){cout << "name:" << obj.name << endl;}
  36. };
  38. typedef struct zoo_obj s_zoo_obj;
  39. typedef zoo_obj_1 c_zoo_obj;
  41. int main(void){
  43.         s_zoo_obj s_obj = {animal,"dog",say};
  44.         zoo_obj_1 c_obj = {animal,"cat"};
  46.         cout << "struct size:" << sizeof(struct zoo_obj) << endl;
  47.         cout << "clsas size:" << sizeof( zoo_obj_1) << endl;
  49.         s_obj.say(s_obj);
  50.         c_obj.say(c_obj);
  52. }
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>
  5. using namespace std;
  7. enum zoo_obj_kind{
  8.         null = 0,
  9. #define null null
  10.         no = 0,
  11. #define no no
  12.         animal = 2,
  13. #define animal animal
  14.         plant = 4,
  15. #define plant plant
  16.         others = 8
  17. #define others others
  19. };
  21. struct zoo_obj{
  22.         zoo_obj_kind zo_kind;
  23.         char name [40];
  24.         void (*say)(struct zoo_obj *);
  25. };
  26. void say(struct zoo_obj *obj){
  27.         !obj
  28.         ? printf("null ")
  29.         : printf("name:%s ",obj->name);
  31. }
  32. class zoo_obj_1{
  33.         public:
  34.         zoo_obj_kind zo_kind;
  35.         char name [40];
  36.         void say(){cout << "name:" << name << endl;}
  37.         void say(zoo_obj_1 *obj){
  38.                 !obj
  39.                 ? cout << "null "
  40.                 : cout << "name:" << obj->name << endl;
  41.         }
  42. };
  44. typedef struct zoo_obj s_zoo_obj;
  45. typedef zoo_obj_1 c_zoo_obj;
  47. int main(void){
  49.         s_zoo_obj s_obj = {animal,"dog",say};
  50.         zoo_obj_1 c_obj = {animal,"cat"};
  52.         cout << "struct size:" << sizeof(struct zoo_obj) << endl;
  53.         cout << "clsas size:" << sizeof( zoo_obj_1) << endl;
  55.         s_obj.say(&s_obj);
  56.         c_obj.say(&c_obj);
  58.         s_obj.say(NULL);
  59.         c_obj.say(NULL);
  61. }
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。
 
 
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原文地址：https://www.cnblogs.com/timssd/p/4781105.html