[Boost-users] Re: Re: Guidelines for effective exception usage

23 Aug 2004

      "Stephen torri"  wrote in message
news:1093236056.8377.60.camel@base.torri.org...
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On Sun, 2004-08-22 at 23:41, Jonathan Turkanis wrote:
...
"Stephen torri"  wrote in message
news:1093230456.8377.44.camel@base.torri.org...
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Are there any guidelines on where and when to use exceptions?
See http://www.boost.org/more/error_handling.html
Thanks for the link. I had already found this link but was confused
on
some of advice it gave. The question below are some of my confusion
about using exceptions wisely. What I am seeking for each of them is
an
example explaining how it implements a solution.
1)  Use virutal inheritance. I see the example and can understand
why
its wrong I just do not understand how to fix it.
...
2) Don't embed a std::string ... How can I use the data I have at
I believe in the example the fix is to use virtual inheritance in the
definitions of  my_exc1 and my_exc2, so that later someone can derive
from both. Using virtual inheritance in the definition of  your_exc3
doen't help. I see that this advice is not followed consistently
within boost (Robert Ramey's serialization library is the only case I
can find). But it's still good advice, I think.

the
...
point of the error safely? I want to provide a debug message to the
user
that will lead them to the answer. This affects 6) Expose relevant
information about the cause of the error.
It's not always possible to satisfy condition (2), but you should do
it whenever possible.
...
In my project I have a base class called BaseException that inherits
from std::exception.
...
class DataTypeException : public BaseException
{
DataTypeException (std::string msg)
: Base_Exception(),
  m_msg(msg)
{}
// Specify virtual functions?
virtual const char* what() const throw()
{
    try
      {
        std::stringstream output;
        output << m_exception_name << ": " << m_message.c_str()
               << std::endl;
         return (output.str()).c_str();
         }
catch(std::exception &)
        {
        return m_exception_name;
        }
}
  private:
std::string m_msg;
};
Often you can get away with:

class Data_Exception : public std::exception {
public:
     Data_Exception(int code) : code_(code) { }
     virtual const char* what() const throw()
     {
          [return result of looking up code in a table of error
messages.]
     }
private:
     int code;
};

As I said, this isn't always sufficient, but it often is.

Jonathan