How to handle exceptions in C++ Lambda expressions?

C++ Exception handling in Lambda expressions does not have its own scope, and exceptions are not caught by default. To catch exceptions, you can use the Lambda expression catching syntax, which allows a Lambda expression to capture a variable within its definition scope for exception handling in a try-catch block.

Exception handling in C++ Lambda expressions

Lambda expressions are a simplified anonymous function syntax for defining code block. They are often used to replace traditional functions or to be passed as input to other functions. While lambda expressions are very useful, handling exceptions in them can be challenging.

Understanding exception handling in Lambda expressions

When handling exceptions in Lambda expressions, you need to consider the following key points:

• Lambda expressions do not have their own scope. They inherit variables and exception handlers from the function in which they are defined.
• By default, Lambda expressions do not catch exceptions. If they don't catch the exception, they pass it to the calling function.

Catching Exceptions

To catch exceptions in Lambda expressions, you can use the Lambda expression catching syntax introduced in C++11. This syntax allows a lambda expression to capture variables within its definition scope.

The following is an example of a Lambda expression that catches an exception:

auto lambda = [function]() -> int {
  try {
    // 业务逻辑
  } catch (const std::exception& e) {
    // 异常处理代码
    return -1;
  }
};

In this example, the Lambda expression captures the function and try-catch Exception handling for its call in the block. If an exception occurs, the lambda expression returns -1.

Practical Case

Consider the following case that requires extensive data processing:

std::vector<int> numbers = {1, 2, 3, 4, 5};

int sum = std::accumulate(numbers.begin(), numbers.end(), 0, [](int a, int b) {
  try {
    if (b == 0) {
      throw std::runtime_error("除以零");
    }
    return a / b;
  } catch (const std::exception& e) {
    std::cerr << "异常信息：" << e.what() << std::endl;
    return 0;
  }
});

In this example, the Lambda expression captures the The range to iterate over the numbers vector provided in std::accumulate. The lambda expression attempts to calculate the quotient between each element and throws an exception if b is 0. If an exception occurs, the lambda expression prints an exception message and returns 0.

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