The constructor is used to initialize the object, and the destructor is used to clean up resources. The constructor is automatically called when the object is created, and has no return value and can be overloaded, such as the default constructor Person() and the parameter constructor Person(string name); if the constructor is not customized, the compiler will generate the default version. The destructor is automatically called at the end of the object's life cycle and is used to release resources. It is not overloadable, such as ~FileHandler(). In terms of call order, member variables are constructed before the class they belong to, and destruction is the opposite. For example, the construction of member A in class B occurs before the B construct, and destruction is after it.

The constructor and the precipitation function are the core parts of the C class design, which are responsible for the initialization and cleaning of objects respectively. Understanding the role and call timing of these two functions is very important for writing safe and efficient C programs.

Constructor: Automatically call when creating an object

The constructor is automatically executed when creating an object, and is mainly used to set the initial state of the object. It has no return value type and the name must be the same as the class name. There can be multiple constructors (overloads) to select the appropriate version according to the different parameters passed in.

For example:

 class Person {
public:
    Person() { cout << "default constructor" << endl; }
    Person(string name) : name(name) { cout << "Constructor with Parameters" << endl; }
private:
    string name;
};

Common ways of using include:

• Default constructor: Person p;
• Parameter constructor: Person p("Tom");

Note: If you do not write the constructor yourself, the compiler will automatically generate a default constructor. But as long as you define any constructor, the default one will not be generated.

Destructor: Automatically call before the end of the object's life cycle

The destructor is used to free up resources occupied by the object, such as closing files, freeing memory, etc. Its name is to add a ~ to the class name, which cannot have parameters and cannot be overloaded.

Example:

 class FileHandler {
public:
    FileHandler(const string& filename) {
        // Open file logic}
    ~FileHandler() {
        // Close file logic cout << "Destructor call, free resource" << endl;
    }
};

Destructors usually do not require manual calls and will be automatically triggered in the following situations:

• Local objects leave scope
• Use delete to delete dynamically allocated objects
• Internal elements will also be destructed when containers are destroyed

If your class involves resource management, be sure to remember to write a destructor, otherwise it will easily cause memory leakage or resource not released.

Pay special attention to the order of constructing and destructuring

When an object is a member variable of a certain class, the construction order is first the parent class and then the member variable, and finally the constructor of the current class; the destruction order is completely opposite.

For example:

 class A {
public:
    A() { cout << "A construct" << endl; }
    ~A() { cout << "A destructuring" << endl; }
};

class B {
public:
    B() { cout << "B Construct" << endl; }
    ~B() { cout << "B destruction" << endl; }
private:
    A a;
};

int main() {
    B b;
}

The output result is:

 A Construct B Construct B Destruction A Destruction

This indicates that the construction of the member variable occurs before the constructor of the class, and the destructor follows it.

Basically that's all. Although the mechanism of constructors and destructors is simple, they often need to be considered in actual development in conjunction with resource management and inheritance structure. If you are not careful, you may cause problems, such as shallow copy resulting in repeated releases, forgetting to release resources, etc. As long as you master the basic principles and practice more with examples, you can use them proficiently.

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