[geos-devel] GEOSException is incompatible with std::exception

[strk at refractions.net]

I've changed GEOSException to derive from std::runtime_exception
and to use initialization list for construction.
Unfortunately I still get the 'unstable' bug.

If other people wants to test this, one of the sympthoms
can be seen by running ./XMLTester TestValid.xml with
and w/out valgrind.

The 'valgrind-equipped' run will result in NO failures.
The 'valgrind-less' run will result in 2 failures (at least here).

Other cases are welcome.

--strk;


On Tue, Apr 04, 2006 at 09:08:59AM +0200, strk at refractions.net wrote:
> Good catch Mateus, anyway there's no std::exception(const char*)
> interface in my STL implementation (GCC 3.3).
> 
> Here it is:
> 
>   /**
>    *  @brief Base class for all library exceptions.
>    *
>    *  This is the base class for all exceptions thrown by the standard
>    *  library, and by certain language expressions.  You are free to derive
>    *  your own %exception classes, or use a different hierarchy, or to
>    *  throw non-class data (e.g., fundamental types).
>    */
>   class exception
>   {
>   public:
>     exception() throw() { }
>     virtual ~exception() throw();
>     /** Returns a C-style character string describing the general cause
>      *  of the current error.  */
>     virtual const char* what() const throw();
>   };
> 
> We can pick one of the derivated classes like runtime_exception
> insted. That one allows contruction taking 'const string&'.
> It's defined in <stdexcept>.
> What do you think ?
> 
> --strk;
>  
> On Tue, Apr 04, 2006 at 12:09:59AM +0200, Mateusz Å?oskot wrote:
> > Hi,
> > 
> > GEOSException class and all its derivatives is incompatible with
> > std::exception.
> > GEOSException is derived from std::exception but it does not make much
> > sense. It even introduces many confusions.
> > 
> > GEOSException has its own member to store message GEOSException::txt.
> > But std::exception has it's own member storing exception message.
> > It also has it's own version of what() function that returns
> > GEOSException::txt but this what() has nothing to do with that one
> > provided by std::exception.
> > 
> > The main problem is that exception details are not available through
> > std::exception interface.
> > Simply, this structure is a kind of two types in one, but every of this
> > participator is completely separated from another one.
> > 
> > Here is illustration of the problem:
> > 
> > try
> > {
> >    throw geos::util::GEOSException("This is a message from GEOS.");
> > }
> > catch (std::exception const& e)
> > {
> >    std::string msg = e.what();
> >    std::cout << msg << std::endl; <--- BUM! BUM! BUM!
> > }
> > 
> > In the example above, exceptions are catched through base
> > std::exception. It's very common situation.
> > The problem is that e.what() returns null pointer.
> > std::exception member of string message is not initialized during
> > construction of GEOSException. This is a bug.
> > 
> > This example illustrates that deriving GEOSException from std::exception
> > has no effect at all. std::exception type is completely unused.
> > 
> > My suggestions are:
> > 1. To remove GEOSException::txt
> > 
> > 2. To use std::exception buffer member for message (in VC++ version of
> > STL it's private member std::exception::_m_what declared as:
> > const char *_m_what;
> > 
> > 3. To initialize call base class (std::exception) constructor during
> > construction of GEOSException using initializers list:
> > 
> > class GEOSException : public std::exception
> > {
> > public:
> >    GEOSException(char const* msg) : std::exception(msg) {}
> >    GEOSException(std::string const& msg)
> >       : std::exception(msg.c_str())
> >    {}
> >    virtual ~GEOSException() {}
> > };
> > 
> > 4. Use initializers list in every class derived from GEOSException,
> > so every time std::exception's message member will be initialized.
> > 
> > Here is usage example that proofs it fixes the problem I introduced:
> > 
> > ///////////////////////////////////////////////////////////
> > #include <iostream>
> > #include <string>
> > #include <exception>
> > 
> > class GEOSException : public std::exception
> > {
> > public:
> >    GEOSException(char const* msg) : std::exception(msg) {}
> >    GEOSException(std::string const& msg)
> >       : std::exception(msg.c_str())
> >    {}
> >    virtual ~GEOSException() {}
> > };
> > 
> > int main()
> > {
> >    try
> >    {
> >       throw GEOSException("This is a message from GEOS.");
> >    }
> >    catch (std::exception const& e)
> >    {
> >       std::string msg = e.what();
> >       std::cout << msg << std::endl;
> >    }
> > 
> >    try
> >    {
> >       std::string msg("This is a std::string message from GEOS.");
> >       throw GEOSException(msg);
> >    }
> >    catch (std::exception const& e)
> >    {
> >       std::string msg = e.what();
> >       std::cout << msg << std::endl;
> >    }
> > 
> >    return 0;
> > }
> > ///////////////////////////////////////////////////////////
> > 
> > 
> > Cheers
> > -- 
> > Mateusz Łoskot
> > http://mateusz.loskot.net
> > 
> > _______________________________________________
> > geos-devel mailing list
> > geos-devel at geos.refractions.net
> > http://geos.refractions.net/mailman/listinfo/geos-devel
> 
> -- 
> 
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