How to flush the ostream when application crash

I have a ostream-based subclass which captures debug messages of my program.

/** @brief Customized output stream with "tee" feature */
template <typename CharT, typename Traits = std::char_traits<CharT> >
class basic_tostream : public std::basic_ostream<CharT, Traits> {
public:
    basic_tostream(std::basic_ostream<CharT, Traits> & o1, /**< main ostream */
                   std::basic_ostream<CharT, Traits> & o2  /**< teed ostream */)
    : std::basic_ostream<CharT, Traits>(&tbuf), tbuf(o1.rdbuf(), o2.rdbuf())
    { /* empty */ }

private:
    tee_outbuf<CharT, Traits> tbuf;
}; // end_class: basic_tostream

How I use this class:

std::ofstream debugFile("debug.txt")
tostream tout(std::cout, debugFile);
/* computation */
tout << "message\n";
/* other computation */

Issue: The class work fine when the application exits normally. But in case of crashing (e.g. array index out of bound, etc), the 'tout' did print out all message to console, but the 'debugFile' does not capture all the printout.

Question: So, how to properly flush the ostream buffer to output file in case when the application crash?

Solution

One way is to use a crash handler. In windows, this is in the form of dbghlp.dll and the just-in-time debugging subsystem.

But by far the easiest way is to flush on every message in one of two ways:

Keep the file open, and call flush after every message.
Open the file in append mode, write, and close the file every time you write a message.

I believe that using endl instead of "\n" will implicitly flush.