Creating new exception

grishaoks · 02-22-2009, 04:28 PM

Hello,

I have a c++ class:

Code:

#ifndef WRONGPARAMETEREXCEPTION_H_

#define WRONGPARAMETEREXCEPTION_H_



#include <iostream>

#include <exception>

#include <string>

using namespace std;



#pragma once



class WrongParameterException: public exception

{

	public:

		WrongParameterException(char* message): exception(message) {};

		virtual ~WrongParameterException() throw() {};

}; 



#endif

when I try to compile it, the compiler gives me this error:

WrongParameterException.h: In constructor ‘WrongParameterException::WrongParameterException(char*)’:
WrongParameterException.h:14: error: no matching function for call to ‘std::exception::exception(char*&)’
/usr/include/c++/4.3/exception:59: note: candidates are: std::exception::exception()
/usr/include/c++/4.3/exception:57: note: std::exception::exception(const std::exception&)

Can anyone tell me what am I doing wrong? I tried changing the message variable to "string" or "const string" or "const string&" but it didnt help..

Here is how I use the new exception that I created from main:

Code:

try

	{

		if ((strToInt1 == -1) || (parameters[1] == NULL) || (strToInt3 == -1) || (parameters[3] != NULL))

		{

			throw WrongParameterException("Error in the config or commands file");

		}

	}

	catch(WrongParameterException e)

	{

		log.addMsg(e.what());

	}

Thanks in advance,

Greg

paulsm4 · 02-22-2009, 11:31 PM

Hi -

I think the basic problem is that you're passing "char *" (i.e. your parameter "char * message") instead of "exception &".

Theselinks might help:

http://www.cplusplus.com/reference/s...exception.html
http://www.cplusplus.com/doc/tutorial/exceptions.html

grishaoks · 02-23-2009, 12:52 AM

The thing is that I want it to pass a certain message and not a sort of exception so how can I do it without passing it a string or a char*?

paulsm4 · 02-23-2009, 08:26 AM

The thing is, if you say "WrongParameterException" is of type "exception" ... and you need to supply the right constructor for type "exception"!

Of course, there's nothing that says you need to subclass the standard C++ "exception". You don't even need "WrongParameterException" at all. You could simply do this (for example):

Quote:

throw new std::string ("Error in the config or commands file");

But frankly, it's probably cleaner to use standard exceptions (like you started out) ... and simply use them correctly.

IMHO .. PSM

PS:
Personally, I much prefer Java or C# exceptions over ANSI C++...

Biddle · 02-23-2009, 10:25 AM

Simply derive from a runtime_error.
As for throwing a std::string this is very bad advice for a couple of reasons.
1) std::string can throw a bad_alloc exception.
2) you catch based on exception types not messages.

dwhitney67 · 02-23-2009, 10:39 AM

Even though the header file for <exception> exists, I believe that it is more appropriate to include <stdexcept>. The latter includes <exception>.

Also, never specify a "using namespace" in a header file.

Here's a working solution to your initial query:

Code:

#include <stdexcept>


class WrongParameterException : public std::exception
{
  public:
    WrongParameterException(const char* message) : m_msg(message) {}

    virtual ~WrongParameterException() throw() {}

    virtual const char* what() const throw() {return m_msg;}

  private:
    const char* m_msg;
};


// test
//
#include <iostream>

int main()
{
  try
  {
    throw WrongParameterException("test");
  }
  catch (WrongParameterException& wpe)
  {
    std::cerr << "Exception: " << wpe.what() << std::endl;
  }
}

Note that std::exception does not have an attribute to store a message. Think of it more as an "interface", but with a public constructor that accepts no args.