c++ - C++::自定义异常，未捕获变量消息(<< 运算符)

Question

您好，我目前的异常类/宏有问题。

所以首先是一个示例文件来说明我的意思。

#include <iostream>
#include <string>

class ExceptionHelper : public std::exception {
public:
  ExceptionHelper(std::string msg) : std::exception(), msg_(msg) {}

  ExceptionHelper operator<<(std::string const &value) {
    msg_.append(" :: ");
    msg_.append(value);
    return ExceptionHelper(msg_);
  }

  virtual const char *what() const throw() { return msg_.c_str(); }

private:
  std::string msg_;
};

#define DEFINE_EXCEPTION(ClassName, Message)                                   \
  class ClassName : public ExceptionHelper {                                   \
  public:                                                                      \
    ClassName(std::string msg = Message) : ExceptionHelper(msg) {}             \
  };

DEFINE_EXCEPTION(Test, "Testmessage")

int main() {
  try {
    throw Test();
  } catch (Test &e) {
    std::cout << "I was caught 1 " << e.what() << std::endl;
  }

  try {
    throw(Test() << "Something added");
  } catch (Test &e) {
    std::cout << "I was caught 2 " << e.what();
  } catch (std::exception &e) {
    std::cout << "should not be called " << e.what() << std::endl;
  }

  try {
    Test t;
    t << "Something added";
    throw t;
  } catch (Test &e) {
    std::cout << "I was caught 3 " << e.what();
  } catch (std::exception &e) {
    std::cout << "should not be called2" << e.what() << std::endl;
  }
}

<< 运算符的不同版本(对输出没有影响):

ExceptionHelper& operator<<(std::string const &value) {
        msg_.append(" :: ");
        msg_.append(value);
        return *this;
      }
ExceptionHelper operator<<(std::string const &value) {
            msg_.append(" :: ");
            msg_.append(value);
            return *this;
          }

输出:

I was caught 1 Testmessage
should not be called Testmessage :: Something added
I was caught 3 Testmessage :: Something added

想要的输出:

I was caught 1 Testmessage
I was caught 2 Testmessage :: Something added
I was caught 3 Testmessage :: Something added

所以我想用我的 DEFINE_EXCEPTION 宏创建特殊异常类，效果很好。

我现在想向新的异常类型添加额外的信息。 (这对于调试很方便，因为它允许我编写类似 throw Test() << "Variable x : "+ std::to_string(x))

这在 main 方法中的情况 2 中显示。这里只捕获 std::exception 而不是 Test 异常。

如果我像在主要的第三个例子中那样做，它工作正常。

我在 << 运算符上尝试了很多样式，但我发现没有哪个会产生影响。

我会对允许该语法的解决方案感兴趣。也欢迎提供为什么这不起作用的信息。

Answer 1

感谢您的提示 :)...漫长的一天。

如果有人对工作版本感兴趣，请点击此处。

class ExceptionHelper : public std::exception {
public:
  ExceptionHelper(std::string msg) : std::exception(), msg_(msg) {}
  virtual const char *what() const throw() { return msg_.c_str(); }

protected:
  std::string msg_;
};

#define DEFINE_EXCEPTION(ClassName, Message)                                   \
  class ClassName : public ExceptionHelper {                                   \
  public:                                                                      \
    ClassName(std::string msg = Message) : ExceptionHelper(msg) {}             \
                                                                               \
    template<class T>                                                          \
    ClassName &operator<<(T const &value) {                                    \
      msg_.append(" :: ");                                                     \
      msg_.append(value);                                                      \
      return *this;                                                            \
    }                                                                          \
  };