Catch Multiple Custom Exceptions? - C++

Question

I'm a student in my first C++ programming class, and I'm working on a project where we have to create multiple custom exception classes, and then in one of our event handlers, use a try/catch block to handle them appropriately.

My question is: How do I catch my multiple custom exceptions in my try/catch block? GetMessage() is a custom method in my exception classes that returns the exception explanation as a std::string. Below I've included all the relevant code from my project.

Thanks for your help!

try/catch block

---

    // 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() Method

---

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!");
}

Just one of my custom exception classes, the others have the same structure as this one

---

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

When templates can't, macros save the day. The solution is taken from Boost. It boils to 7 lines of code.

/// @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