C语言中结构体和类的区别及使用场景是什么？

C语言中结构体和类的区别及使用场景是什么？

结构体基本概念：

1. 结构体定义

   c
   struct Point {
       int x;
       int y;
   };
   
   struct Point p1 = {10, 20};
   struct Point p2 = {.x = 30, .y = 40};

2. 结构体指针

   c
   struct Point *ptr = &p1;
   ptr->x = 50;
   ptr->y = 60;

与类的对比：

1. 数据封装

   c
   // C语言结构体
   struct Rectangle {
       int width;
       int height;
   };
   
   // C++类
   class Rectangle {
   private:
       int width;
       int height;
   public:
       Rectangle(int w, int h) : width(w), height(h) {}
       int area() { return width * height; }
   };

2. 方法定义

   c
   // C语言：使用函数指针
   struct Shape {
       int (*area)(struct Shape*);
       int (*perimeter)(struct Shape*);
   };
   
   int rectangle_area(struct Shape *s) {
       struct Rectangle *r = (struct Rectangle*)s;
       return r->width * r->height;
   }
   
   // C++：成员函数
   class Shape {
   public:
       virtual int area() = 0;
       virtual int perimeter() = 0;
   };

3. 构造和析构

   c
   // C语言：手动初始化
   struct Point create_point(int x, int y) {
       struct Point p = {x, y};
       return p;
   }
   
   void destroy_point(struct Point *p) {
       // 手动清理资源
   }
   
   // C++：自动构造和析构
   class Point {
   public:
       Point(int x, int y) : x(x), y(y) {}
       ~Point() {}
   private:
       int x, y;
   };

使用场景：

1. 数据结构

   c
   struct Node {
       int data;
       struct Node *next;
   };
   
   struct LinkedList {
       struct Node *head;
       int size;
   };

2. 配置管理

   c
   struct Config {
       char server[256];
       int port;
       int timeout;
       int max_connections;
   };
   
   struct Config load_config(const char *filename);

3. 网络协议

   c
   struct PacketHeader {
       unsigned int version : 4;
       unsigned int type : 4;
       unsigned int length : 16;
       unsigned int checksum : 8;
   };

高级特性：

1. 结构体嵌套

   c
   struct Address {
       char street[100];
       char city[50];
       char country[50];
   };
   
   struct Person {
       char name[50];
       int age;
       struct Address address;
   };
   
   struct Person person = {
       .name = "John Doe",
       .age = 30,
       .address = {
           .street = "123 Main St",
           .city = "New York",
           .country = "USA"
       }
   };

2. 结构体数组

   c
   struct Student {
       int id;
       char name[50];
       float score;
   };
   
   struct Student students[100];
   students[0].id = 1;
   strcpy(students[0].name, "Alice");
   students[0].score = 95.5;

3. 灵活数组成员

   c
   struct String {
       size_t length;
       char data[];  // 灵活数组成员
   };
   
   struct String *create_string(const char *str) {
       size_t len = strlen(str);
       struct String *s = malloc(sizeof(struct String) + len + 1);
       s->length = len;
       strcpy(s->data, str);
       return s;
   }

最佳实践：

1. 命名约定

   c
   struct Point {
       int x;
       int y;
   };
   
   typedef struct Point Point;
   
   Point p1 = {10, 20};

2. 初始化函数

   c
   struct Point point_create(int x, int y) {
       struct Point p = {x, y};
       return p;
   }
   
   struct Point p = point_create(10, 20);

3. 内存管理

   c
   struct Point *point_alloc(int x, int y) {
       struct Point *p = malloc(sizeof(struct Point));
       if (p) {
           p->x = x;
           p->y = y;
       }
       return p;
   }
   
   void point_free(struct Point *p) {
       free(p);
   }

注意事项：

1. 内存对齐

   c
   struct Example {
       char c;      // 1字节 + 3字节填充
       int i;       // 4字节
   };              // 总大小: 8字节

2. 结构体赋值

   c
   struct Point p1 = {10, 20};
   struct Point p2 = p1;  // 浅拷贝

3. 结构体比较

   c
   struct Point p1 = {10, 20};
   struct Point p2 = {10, 20};
   
   // 错误：不能直接比较结构体
   // if (p1 == p2) { }
   
   // 正确：逐个成员比较
   if (p1.x == p2.x && p1.y == p2.y) {
       printf("Equal\n");
   }