What type of exception should I throw?

Asked 2009-07-21T06:39:44.170

After going through some links on exception handling (1, 2, and 3), I know that C++ programs can throw pretty much anything as exceptions (int, char*, string, exception class). I know that std::exception is the base class for standard exceptions thrown by the program. However, I'm trying to design a try...catch block as such:

try
{
    MyFunc();
}
catch (certain exceptions)
{
    // deal with the exception accordingly
}
catch (the rest of the exceptions)
{
    // deal with these accordingly
}

while MyFunc() contains the following:

void MyFunc()
{
    ...
    if (certain condition is true) throw exception;
    ...
}

The trouble is that in that part of MyFunc function, I'm not sure what type of exception I should throw. To keep the code clean by implementing my own exceptions class, I have no idea what would be a good way to implement such exceptions class.

c++ exception

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2 Answers

You would derive your own class from std::exception, so that there is some way of uniformly handling exceptions.

If this seems like overkill, you can throw std::logic_error or one of the other standard exception types intended for applications to use.

You could also use these as base classes for your own more specific exceptions: this saves a little work because they take care of implementing the what method for you.

Note that deep exception hierarchies can be unusable, because you're basically making a guess in advance about how to categorize the errors, and your clients may disagree.

answered 2009-07-21T06:51:38.140

I thought it might be interesting to post some real code for a change. This is the exception class my own utility library uses:

//---------------------------------------------------------------------------
// a_except.h
//
// alib exception handling stuff
//
// Copyright (C) 2008 Neil Butterworth
//---------------------------------------------------------------------------

#ifndef INC_A_EXCEPT_H
#define INC_A_EXCEPT_H

#include "a_base.h"
#include <exception>
#include <sstream>

namespace ALib {

//------------------------------------------------------------------------
// The only exception thrown directly by alib
//------------------------------------------------------------------------

class Exception : public std::exception {

    public:

        Exception( const std::string & msg = "" );
        Exception( const std::string & msg, int line,
                        const std::string & file );

        ~Exception() throw();

        const char *what() const throw();
        const std::string & Msg() const;

        int Line() const;
        const std::string & File() const;

    private:

        std::string mMsg, mFile;
        int mLine;
};

//------------------------------------------------------------------------
// Macro to throw an alib exception with message formatting.
// Remember macro is not in ALib namespace!
//------------------------------------------------------------------------

#define ATHROW( msg )                                               \
{                                                                   \
    std::ostringstream os;                                          \
    os << msg;                                                      \
    throw ALib::Exception( os.str(), __LINE__, __FILE__ );          \
}                                                                   \


}  // namespace

#endif

And this is the .cpp file:

//----------


                        
                        
                            answered 2009-07-21T07:33:47.133



        
        
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