C++ 例外処理はカスタム エラー処理ルーチンをどのようにサポートしますか?

class MyCustomException : public std::exception {
public:
  const char* what() const noexcept override {
    return "This is my custom exception.";
  }
};

throw MyCustomException();

try {
  // 可能抛出异常的代码
} catch (MyCustomException& e) {
  // 处理 MyCustomException 异常
} catch (std::exception& e) {
  // 处理所有其他类型的异常
}

#include <fstream>
#include <iostream>

using namespace std;

// 自定义异常类
class FileOpenException : public std::exception {
public:
  const char* what() const noexcept override {
    return "Could not open the file.";
  }
};

// 打开文件并读取其内容的函数
string read_file(const string& filename) {
  ifstream file(filename);
  if (!file.is_open()) {
    throw FileOpenException();
  }

  string contents;
  string line;
  while (getline(file, line)) {
    contents += line + '\n';
  }
  file.close();

  return contents;
}

int main() {
  try {
    string contents = read_file("file.txt");
    cout << contents << endl;
  } catch (FileOpenException& e) {
    cout << "Error: " << e.what() << endl;
  } catch (std::exception& e) {
    cout << "An unexpected error occurred." << endl;
  }
  
  return 0;
}