C++ polymorphism

Polymorphism is one of the core concepts of object-oriented programming (OOP), which allows objects to exhibit different behaviors under the same operation. In C++, polymorphism is usually implemented through inheritance and virtual functions.

Understanding polymorphism

Imagine a scenario where you have a zoo with various animals such as cats, dogs, birds, etc. Each animal has its own call. Using object-oriented programming, we can create a base class Animalto represent all animals and define a makeSound()virtual function for it. We can then create derived classes such as Cat, , Dogand Bird, and override their makeSound()methods to implement their respective calls.

class Animal {
public:
  virtual void makeSound() = 0; // 虚函数声明
};
 
class Cat : public Animal {
public:
  void makeSound() override {
    cout << "Meow!" << endl;
  }
};
 
class Dog : public Animal {
public:
  void makeSound() override {
    cout << "Woof!" << endl;
  }
};
 
class Bird : public Animal {
public:
  void makeSound() override {
    cout << "Chirp!" << endl;
  }
};

In this example, Animalthe class makeSound()function is declared virtual, which means it can be overridden in derived classes. When we create a Animalpointer or reference of type, we can point to an object of any derived class. Then, makeSound()when the function is called, the actual code executed will depend on the type of object pointed to.

Advantages of polymorphism

• Reusability of code: Polymorphism allows you to create common functions for common base class operations and implement them concretely in derived classes.
• Flexibility: Polymorphism makes your code more flexible because it allows you to choose different behaviors at runtime depending on the actual situation.
• Maintainability: Polymorphism improves the maintainability of your code because it makes it easier to understand and modify.

polymorphic implementation

In C++, the implementation of polymorphism mainly relies on the following two mechanisms:

• Inheritance: As mentioned above, polymorphism is usually implemented through inheritance. Base classes define virtual functions that derived classes can override to implement specific behaviors.
• Virtual function: A virtual function is virtuala member function with keyword. When a virtual function is called, the actual code executed will depend on the type of object pointed to.

Summarize

Polymorphism is a powerful tool in object-oriented programming that allows you to create more flexible and maintainable code. By understanding the basic concepts of polymorphism and how it is implemented, you can improve your programming skills and build more elegant software solutions.

C++ file operations

C++ provides a variety of mechanisms for manipulating files, including creating, reading, writing, and modifying files. Commonly used file manipulation libraries include fstreamand <filesystem>.

1. Use fstreamthe library

fstreamlibrary is one of the most commonly used file manipulation libraries in C++. It provides the following classes:

• ofstream: used to create and write files
• ifstream: used to read files
• fstream: Supports both read and write operations

Example: Create and write a file

#include <iostream>
#include <fstream>
 
using namespace std;
 
int main() {
  // 创建 ofstream 对象并打开文件
  ofstream myFile("myfile.txt");
 
  // 检查文件是否打开成功
  if (myFile.is_open()) {
    // 将文本写入文件
    myFile << "This is a line of text in my file." << endl;
 
    // 关闭文件
    myFile.close();
    cout << "File written successfully." << endl;
  } else {
    cout << "Error opening file." << endl;
  }
 
  return 0;
}

Example: Reading a file

#include <iostream>
#include <fstream>
 
using namespace std;
 
int main() {
  // 创建 ifstream 对象并打开文件
  ifstream myFile("myfile.txt");
 
  // 检查文件是否打开成功
  if (myFile.is_open()) {
    string line;
 
    // 逐行读取文件内容
    while (getline(myFile, line)) {
      cout << line << endl;
    }
 
    // 关闭文件
    myFile.close();
  } else {
    cout << "Error opening file." << endl;
  }
 
  return 0;
}

2. Use <filesystem>the library

C++17 introduced <filesystem>the library, which provides a more modern file operation interface.

Example: Create and write a file

#include <iostream>
#include <filesystem>
 
using namespace std;
namespace fs = std::filesystem;
 
int main() {
  // 创建文件路径
  fs::path myFile("myfile.txt");
 
  // 打开文件并写入文本
  fs::ofstream ofs(myFile);
  if (ofs.is_open()) {
    ofs << "This is a line of text in my file." << endl;
    ofs.close();
  } else {
    cout << "Error opening file." << endl;
  }
 
  return 0;
}

Example: Reading a file

#include <iostream>
#include <filesystem>
 
using namespace std;
namespace fs = std::filesystem;
 
int main() {
  // 创建文件路径
  fs::path myFile("myfile.txt");
 
  // 打开文件并读取内容
  fs::ifstream ifs(myFile);
  if (ifs.is_open()) {
    string line;
    while (getline(ifs, line)) {
      cout << line << endl;
    }
    ifs.close();
  } else {
    cout << "Error opening file." << endl;
  }
 
  return 0;
}

Summarize

C++ provides a variety of file manipulation mechanisms for creating, reading, writing, and modifying files. fstreamLibraries are the traditional choice, while <filesystem>libraries provide a more modern interface. Which library to choose depends on your project needs and personal preference.

Please note that these are just some simple examples. C++ file operations also involve many other advanced features, such as directory manipulation, error handling, and file iteration. It is recommended that you consult the C++ standard library documentation and related tutorials for more information.