[C++11/C++20] Feature introduction

1. Main features of C++11
2. Main features of C++20
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1. Main features of C++11

C++11 is an important standard for the C++ programming language. Released in 2011, it introduces many new features and improvements aimed at improving the performance, readability, and functionality of C++. Here are some of the main features of C++11:

Automatic type inference (Type Inference): auto The keyword allows the compiler to automatically deduce the type of variables, reducing the tediousness of type declarations and improving readability.
```
auto x = 42; // x被推导为int类型
```

Range-based for loops: Simplify the process of iterating over container and array elements.

cppCopy codefor (auto& item : container) 
{
      
      
    // 对每个元素执行操作
}

Lambda expressions: Allow anonymous functions to be defined in code, making functional programming easy.

auto add = [](int x, int y) {
      
       return x + y; };
int result = add(3, 4); // 结果为7

Smart Pointers: Introduced std::shared_ptrand std::unique_ptrto help manage dynamically allocated memory and reduce the risk of memory leaks.
```
std::shared_ptr<int> ptr = std::make_shared<int>(42);
```
Rvalue References: Introduced &&to represent rvalue references, supports move semantics and perfect forwarding, and improves performance.
```
int&& rvalue_ref = 42;
```
nullptr keyword: used to explicitly represent a null pointer, replacing the traditional one NULL.
```
int* ptr = nullptr;
```
New containers: Unordered containers such as , and std::unordered_mapfixed -size arrays are introduced .std::unordered_setstd::array
```
std::unordered_map<std::string, int> my_map;
```
Concurrency support: Multi-thread programming support such as threads, mutexes, and condition variables is introduced.
```
#include <thread>
// 创建线程
std::thread my_thread(my_function);
```
Initializer Lists: Allows the use of initialization lists to initialize arrays, containers, etc.
```
std::vector<int> numbers = {
      
      1, 2, 3, 4};
```
New language features: including constexprfunctions, type aliases, delegate constructors, etc.

C++11 brings many powerful features that improve code readability and performance and make C++ a more modern programming language.

2. Main features of C++20

C++20 is a major standard for the C++ programming language, released in 2020. It introduces many new features and improvements designed to further improve the performance, readability, and functionality of C++. Here are some of the main features of C++20:

Concepts: Concepts are a new language feature that allows programmers to explicitly define type requirements, thereby improving the readability of template code and the quality of error messages.
```
template <typename T>
concept Integral = std::is_integral_v<T>;

template <Integral T>
T add(T a, T b) 
{
      
      
    return a + b;
}
```
Range-enhanced for loop: The range-based for loop has been enhanced to support direct modification of elements in the container.
```
for (auto& item : container | std::views::filter(is_even)) 
{
      
      
    item *= 2;
}
```
Initializer Lists: Allows array-like initializer lists for standard containers and custom classes.
```
std::vector<int> numbers = {
      
      1, 2, 3, 4};
```

Coroutines: Coroutine support is introduced, allowing for more readable and maintainable asynchronous code to be written.

generator<int> generate_numbers() 
{
      
      
    for (int i = 0; i < 10; ++i) 
    {
      
      
        co_yield i;
    }
}

Three-Way Comparison Operator: The operator is introduced <=>to simplify the comparison of custom types.
```
bool operator<=>(const MyClass& other) const = default;
```
Modules: Introduces modular programming to improve code organization and build performance.
```
import module_name;
```
Concurrency enhancements: Introduces a series of new concurrency and parallel programming features, including std::jthread, std::stop_tokenetc.
```
std::jthread my_thread(my_function);
```
String operation enhancements: Introduced support for Unicode string operations, as well as new string search and processing functions.
```
std::string_view str_view = "Hello, C++20";
```
Other improvements: It also includes other small language improvements and standard library enhancements, such as file system support, math library enhancements, etc.

C++20 greatly enriches the C++ language and provides more modern programming tools and performance optimizations, making C++ a more powerful and flexible programming language.

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