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 Åoskot
> http://mateusz.loskot.net
>
> _______________________________________________
> geos-devel mailing list
> geos-devel@geos.refractions.net
> http://geos.refractions.net/mailman/listinfo/geos-devel
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