Usage and characteristics of C++ anonymous functions

Anonymous function, also known as lambda expression, is a function without specifying a name, used for one-time use or passing function pointer. Features include: anonymity, one-time use, closures, return type inference. In practice, it is often used for sorting or other one-time function calls.

C Usage and characteristics of anonymous functions

Anonymous functions, also called Lambda expressions, are Functions without specifying a name are usually used to define one-time-use functions or when a function pointer needs to be passed.

Syntax

The basic syntax of Lambda expression is as follows:

[capture list] (parameters) -> return type { function body }

• capture list: used to capture external Variables, similar to the auto keyword in a function, can specify the variable name or reference to be captured.
• parameters: The parameter list of the Lambda expression.
• return type: The return type of the Lambda expression.
• function body: The function body of the Lambda expression.

Features

• Anonymity: Lambda expressions have no names and can only be referenced through function pointers or other syntax structures. .
• One-time use: Lambda expressions are usually used for one-time use and will generally not be called again after being defined.
• Closure: Lambda expressions can capture external variables to form closures, and the values ​​of external variables can be used.
• Return type inference: The return type of a lambda expression can be inferred by the compiler unless explicitly specified.

Practical case

The following is an example of sorting vectors using Lambda expressions:

#include <vector>
#include <algorithm>

int main() {
  std::vector<int> vec = { 1, 3, 2, 5, 4 };

  // 使用Lambda表达式对向量排序
  std::sort(vec.begin(), vec.end(), [](int a, int b) { return a < b; });

  // 输出排序后的向量
  for (auto& elem : vec) {
    std::cout << elem << " ";
  }
  std::cout << std::endl;

  return 0;
}

Output:

1 2 3 4 5

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