C++中访问结构体成员应该使用点运算符还是箭头运算符

.

->

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->

struct User {
    std::string name;
    int age;
};

User user1; // user1 是一个User类型的对象
user1.name = "Alice";
user1.age = 30;

user1

User

name

age

.

user1.name

user1.age

User* userPtr; // userPtr 是一个指向User类型对象的指针
userPtr = new User(); // 分配内存并让userPtr指向它

// 或者，让指针指向已存在的对象
// userPtr = &user1; 

userPtr

User

userPtr

userPtr

User

User

*

(*userPtr).name = "Bob"; // 先解引用userPtr，得到User对象，再用.访问成员
(*userPtr).age = 25;

->

ptr->member

(*ptr).member

userPtr->name = "Bob"; // 使用箭头运算符直接访问指针指向对象的成员
userPtr->age = 25;

// 记得释放动态分配的内存
delete userPtr;
userPtr = nullptr;

User

user1

user1.name

user1

name

.

User* userPtr

userPtr

User

User

User

userPtr

*userPtr

User

User

(*userPtr).name

->

new

// 动态创建一个User对象
User* dynamicUser = new User{"Grace", 40};
dynamicUser->name = "Grace"; // 访问成员
delete dynamicUser; // 记得释放内存
dynamicUser = nullptr;

// 创建一个User对象的动态数组
User* userArray = new User[10];
userArray[0].name = "Henry"; // 数组元素是对象，用.
(userArray + 1)->name = "Ivy"; // 另一种指针算术访问方式，等同于userArray[1].name
delete[] userArray;
userArray = nullptr;

void printUser(const User* u) { // 接收一个指向User的常量指针
    if (u) { // 良好的实践：检查指针是否为空
        std::cout << "Name: " << u->name << ", Age: " << u->age << std::endl;
    }
}

User myUser{"Frank", 35};
printUser(&myUser); // 传递myUser的地址

class Shape {
public:
    virtual void draw() const = 0; // 虚函数
    virtual ~Shape() = default;
};

class Circle : public Shape {
public:
    void draw() const override { std::cout << "Drawing a Circle." << std::endl; }
};

class Square : public Shape {
public:
    void draw() const override { std::cout << "Drawing a Square." << std::endl; }
};

void renderShape(Shape* s) {
    s->draw(); // 通过基类指针调用派生类的draw()
}

// ...
Shape* myCircle = new Circle();
Shape* mySquare = new Square();
renderShape(myCircle); // 输出: Drawing a Circle.
renderShape(mySquare); // 输出: Drawing a Square.
delete myCircle;
delete mySquare;

struct Node {
    int data;
    Node* next; // 指向下一个节点的指针
};

Node* head = new Node{10, nullptr};
Node* second = new Node{20, nullptr};
head->next = second; // 连接节点
std::cout << head->next->data << std::endl; // 访问下一个节点的数据
// ... 记得释放链表内存

nullptr

User* nullUser = nullptr;
// nullUser->name = "Error"; // 运行时错误，程序崩溃！
// (*nullUser).age = 0;      // 同样会崩溃

new

nullptr

delete

nullptr

nullptr

User userObj;
// userObj->name = "Invalid"; // 编译错误：'->' must be used with a pointer
User* userPtr = &userObj;
// userPtr.name = "Invalid"; // 编译错误：'.' must be used with an object or reference

new

User* tempUser = new User();
tempUser->name = "Temporary";
// ... 做了些操作，然后忘记 delete tempUser;
// 内存泄漏！

nullptr

User* oldUser = new User();
delete oldUser;
// oldUser 此时是一个悬空指针
// oldUser->name = "Dangerous"; // 未定义行为！
oldUser = nullptr; // 良好的实践

std::unique_ptr

std::shared_ptr