Re: std::exception what() method
On Mar 28, 6:31 pm, "petek1976" <pete.karou...@earthlink.net> wrote:
Hi,
I have the following exception class:
#include <string>
#include <exception>
class tcClockSynchException : public std::exception
{
public:
explicit tcClockSynchException(const char *apnMsg) : mcMsg(apnMsg) {}
virtual const char *what() const throw() { return mcMsg.c_str(); }
virtual ~tcClockSynchException() throw() {}
private:
std::string mcMsg;
};
I'm a little worried about the what() method. It isn't clear to me
whether or not I can rely on c_str() to not throw any exceptions,
since the what() method in the base class says it will not throw any
exceptions. Does the standard guarantee that c_str() will not throw
any exceptions? If it doesn't guarantee this what is a better way to
implement my exception class?
In practice I would follow Alex Shulgin's advice and derive your
tcClockSynchException from the appropriate class in <stdexcept>. As an
alternative I would try and anticipate the risk of another exception
being thrown to the construction (or the copy) of your exception
object. One way to do it could be the use of std::vector in place of
std::string to store the error message, as follows:
#include <cstring>
#include <exception>
#include <vector>
class tcClockSynchException : public std::exception {
public:
explicit tcClockSynchException(const char *apnMsg) {
std::size_t len = std::strlen(apnMsg) + 1;
mcMsg.reserve(len);
mcMsg.assign(apnMsg,apnMsg+len);
}
virtual const char *what() const throw() { return &mcMsg[0]; }
virtual ~tcClockSynchException() throw() {}
private:
std::vector<char> mcMsg;
};
Here allocation should be the only operation that could throw and it
should only take place in the call to reserve() and in every call to
the class's implicit copy constructor.
Cheers,
Nicola Musatti
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