Notes on initialization and destruction of C++ container libraries

C++ container library objects are initialized using constructors when they are created. The following constructors are provided: Default Constructor: Creates an empty container. Range constructor: Populates a container from other containers or data structures. Copy constructor: A container that creates copies of other containers. Move constructor: Creates a container with the moved content of other containers, and leaves the other containers empty. The destructor is called when the container object goes out of scope or is explicitly destroyed, releasing the memory associated with the container. Custom destructors are essential to release additional resources (such as file handles or pointers) associated with elements in the container to avoid memory leaks.

Notes on initialization and destruction of C++ container libraries

Objects in C++ container libraries are usually created using specific The constructor does the initialization and the destructor does the destructuring when it goes out of scope. Understanding the initialization and destruction process is critical to managing memory and avoiding resource leaks.

Initialization

The container library provides various constructors to initialize container objects:

• Default constructor: Create an empty container.
• Range constructor: Use an input iterator to populate a container from other containers or data structures.
• Copy constructor: Creates a container that contains copies of other containers.
• Move constructor: Create a container containing the moved content of other containers, and make other containers empty.

Note: For move semantics, the move constructor needs to be explicitly specified as explicit.

Example:

// 默认构造函数
std::vector<int> myVector;

// 范围构造函数
std::vector<int> myVector2(myVector.begin(), myVector.end());

// 拷贝构造函数
std::vector<int> myVector3(myVector2);

// 移动构造函数
std::vector<int> myVector4(std::move(myVector3));

Destruction

Destruction occurs when the container object goes out of scope or is explicitly destroyed The function will be called. The destructor is responsible for releasing the memory associated with the container.

• Default destructor: Release the memory associated with the container object itself.
• Custom destructor: Can release attached resources (for example, file handles or pointers) associated with elements in the container.

Note: Custom destructors are crucial when working with dynamically allocated elements.

Example:

class MyClass {
public:
  ~MyClass() {
    // 释放与对象相关的资源
  }
};

int main() {
  std::vector<MyClass> myVector; // 创建容器
  myVector.emplace_back(); // 动态创建并追加元素
  // ... 代码 ...
  return 0; // 容器对象在超出作用域时析构
}

Practical case

Danger of memory leak:

std::vector<std::ifstream> files; // 文件句柄容器

// 打开文件并追加到容器
files.emplace_back("file1.txt");
files.emplace_back("file2.txt");

// 在没有明确关闭文件的情况下容器超出作用域

Solution: Use a custom destructor to explicitly close the file handle.

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