Re: subclassing std::exception, where to store what() error string?

Please consider the below class MyError. My question is is it safe/
correct to store a std::string in a std::exception subclass and then
return string::c_str() on exception::what(). If not what is the
correct way to do this then? Thanks, Andrew.

#include <exception>
#include <string>
#include <sstream>

using namespace std;

class MyError : public exception
{
public:
        MyError(A a, B b, C c)
        {
                ostringstream os;

                os << "MyError occured because A =" << =

b.str() << " and C = " << c.str() << endl;

                m_sWhat = os.str();
        }

    virtual const char* what() const throw() { return
m_sWhat.c_str(); }

    virtual ~MyError() throw() {}

private:
        string m_sWhat;

};