Question

我是第一个C ++编程类的学生，我正在开发一个项目，我们必须创建多个自定义异常类，然后在我们的一个事件处理程序中使用try/catch块适当地处理它们。

我的问题是：如何在try/catch块中捕获多个自定义异常？ GetMessage()是我的异常类中的自定义方法，它将异常解释作为std::string返回。下面我已经包含了我项目中的所有相关代码。

感谢您的帮助！

尝试/捕获阻止

    // This is in one of my event handlers, newEnd is a wxTextCtrl
try {
    first.ValidateData();
    newEndT = first.ComputeEndTime();
    *newEnd << newEndT;
}
catch (// don't know what do to here) {
    wxMessageBox(_(e.GetMessage()), 
                 _("Something Went Wrong!"),
                 wxOK | wxICON_INFORMATION, this);;
}

ValidateData（）方法

void Time::ValidateData()
{
    int startHours, startMins, endHours, endMins;

    startHours = startTime / MINUTES_TO_HOURS;
    startMins = startTime % MINUTES_TO_HOURS;
    endHours = endTime / MINUTES_TO_HOURS;
    endMins = endTime % MINUTES_TO_HOURS;

    if (!(startHours <= HOURS_MAX && startHours >= HOURS_MIN))
        throw new HourOutOfRangeException("Beginning Time Hour Out of Range!");
    if (!(endHours <= HOURS_MAX && endHours >= HOURS_MIN))
        throw new HourOutOfRangeException("Ending Time Hour Out of Range!");
    if (!(startMins <= MINUTE_MAX && startMins >= MINUTE_MIN))
        throw new MinuteOutOfRangeException("Starting Time Minute Out of    Range!");
    if (!(endMins <= MINUTE_MAX && endMins >= MINUTE_MIN))
        throw new MinuteOutOfRangeException("Ending Time Minute Out of Range!");
    if(!(timeDifference <= P_MAX && timeDifference >= P_MIN))
        throw new PercentageOutOfRangeException("Percentage Change Out of Range!");
    if (!(startTime < endTime))
        throw new StartEndException("Start Time Cannot Be Less Than End Time!");
}

只是我的一个自定义异常类，其他类似于此结构

class HourOutOfRangeException
{
public:
        // param constructor
        // initializes message to passed paramater
        // preconditions - param will be a string
        // postconditions - message will be initialized
        // params a string
        // no return type
        HourOutOfRangeException(string pMessage) : message(pMessage) {}
        // GetMessage is getter for var message
        // params none
        // preconditions - none
        // postconditions - none
        // returns string
        string GetMessage() { return message; }
        // destructor
        ~HourOutOfRangeException() {}
private:
        string message;
};

Answer 1

如果您有多种异常类型，并且假设存在异常层次结构（并且所有异常都是从std::exception的某些子类公开派生的），则从最具体的开始，继续更一般：

try
{
    // throws something
}
catch ( const MostSpecificException& e )
{
    // handle custom exception
}
catch ( const LessSpecificException& e )
{
    // handle custom exception
}
catch ( const std::exception& e )
{
    // standard exceptions
}
catch ( ... )
{
    // everything else
}

另一方面，如果您只对错误消息感兴趣 - throw相同的异常，请说std::runtime_error使用不同的消息，然后catch：

try
{
    // code throws some subclass of std::exception
}
catch ( const std::exception& e )
{
    std::cerr << "ERROR: " << e.what() << std::endl;
}

还要记住 - 按值抛出，按[const]引用捕获。

Answer 2

您应该创建一个基本异常类，并从中获取所有特定异常：

class BaseException { };
class HourOutOfRangeException : public BaseException { };
class MinuteOutOfRangeException : public BaseException { };

然后，您可以在一个catch块中捕获所有这些：

catch (const BaseException& e) { }

如果您希望能够拨打GetMessage，则需要：

将该逻辑放入BaseException或
在GetMessage中使BaseException成为虚拟成员函数，并在每个派生的异常类中覆盖它。

您也可以考虑将异常派生自标准库异常之一，例如std::runtime_error，并使用惯用what()成员函数代替GetMessage()。

Answer 3

从具有虚拟方法BaseException的公共基类GetMessage()派生所有异常。

然后catch(const BaseException& e)。

Answer 4

我今天遇到了类似的问题，但事实证明我并不需要我的解决方案来解决我的问题。老实说，我无法想到真实的用例（日志记录？），我在代码中找不到它的用处。

无论如何，这是一种带有类型列表的方法（需要C ++ 11）。我认为这种方法的优点是不需要为自定义异常提供公共基类（除了std :: exception，可能？）。换句话说，它不会干扰您的异常层次结构。

可能会有一些我不知道的微妙错误。

#include <type_traits>
#include <exception>

/// Helper class to handle multiple specific exception types
/// in cases when inheritance based approach would catch exceptions
/// that are not meant to be caught.
///
/// If the body of exception handling code is the same
/// for several exceptions,
/// these exceptions can be joined into one catch.
///
/// Only message data of the caught exception is provided.
///
/// @tparam T  Exception types.
/// @tparam Ts  At least one more exception type is required.
template <class T, class... Ts>
class MultiCatch;

/// Terminal case that holds the message.
/// ``void`` needs to be given as terminal explicitly.
template <>
class MultiCatch<void> {
 protected:
  explicit MultiCatch(const char* err_msg) : msg(err_msg) {}
  const char* msg;
};

template <class T, class... Ts>
class MultiCatch : public MultiCatch<Ts...> {
  static_assert(std::is_base_of<std::exception, T>::value, "Not an exception");

 public:
  using MultiCatch<Ts...>::MultiCatch;

  /// Implicit conversion from the guest exception.
  MultiCatch(const T& error) : MultiCatch<Ts...>(error.what()) {}  // NOLINT

  /// @returns The message of the original exception.
  const char* what() const noexcept {
    return MultiCatch<void>::msg;
  }
};

/// To avoid explicit ``void`` in the type list.
template <class... Ts>
using OneOf = MultiCatch<Ts..., void>;

/// Contrived example.
void foo() {
  try {
    bar();  // May throw three or more sibling or unrelated exceptions.
  } catch (const OneOf<IOError, OutOfMemory>& err) {
    log() << "External failure: " << err.what();

    throw;  // Throw the original exception.
  }
}

Answer 5

当模板无法使用时，宏可以保存当天。解决方案取自Boost。它可以归结为7行代码。

/// @file multicatch.hpp
#include <boost/preprocessor/variadic/to_list.hpp>
#include <boost/preprocessor/list/for_each.hpp>

/// Callers must define CATCH_BODY(err) to handle the error,
/// they can redefine the CATCH itself, but it is not as convenient. 
#define CATCH(R, _, T) \
  catch (T & err) {    \
    CATCH_BODY(err)    \
  }
/// Generates catches for multiple exception types
/// with the same error handling body.
#define MULTICATCH(...) \
  BOOST_PP_LIST_FOR_EACH(CATCH, _, BOOST_PP_VARIADIC_TO_LIST(__VA_ARGS__))
// end of file multicatch.hpp

/// @file app.cc
#include "multicatch.hpp"

// Contrived example.
/// Supply the error handling logic.
#define CATCH_BODY(err)                        \
  log() << "External failure: " << err.what(); \
  throw;

void foo() {
  try {
    bar();  // May throw three or more sibling or unrelated exceptions.
  }
  MULTICATCH(IOError, OutOfMemory)
}

#undef CATCH_BODY

Answer 6

我遇到了同样的问题，这就是我最终得到的结果：

  std::shared_ptr<MappedImage> MappedImage::get(const std::string & image_dir,
                                                const std::string & name,
                                                const Packet::Checksum & checksum) {
    try {
      return std::shared_ptr<MappedImage>(images_.at(checksum));
    } catch (std::out_of_range) {
    } catch (std::bad_weak_ptr) {
    }
    std::shared_ptr<MappedImage> img =
      std::make_shared<MappedImage>(image_dir, name, checksum);
    images_[checksum_] = img;
    return img;
  }

就我而言，该函数在没有异常时返回。因此，我实际上不必在捕获范围内做任何事情，而可以在尝试之外进行工作。

Answer 7



#include <iostream> 
void test(int x)`
{
try{
if(x==1)
throw (1);
else if(x==2)
    throw (2.0);
}
catch(int a)
{
cout<<"It's Integer";
}
catch(double b)
{
cout<<"it's Double";
}
}
int main(){
cout<<" x=1";
test(1);
cout<<"X=2";
test(2.0);
return 0;
}`

捕获多个自定义异常？ - C ++

7 个答案: