I'm convinced at this point that I should be creating subclasses of std::exception for all my exception throwing needs. Now I'm looking at how to override the what method.

The situation that I'm facing, it would be really handy if the string what returns be dynamic. Some pieces of code parse an XML file for example, and adding a position or line number to the error message is useful to me.

What I'd like to know:

• what returns a const char *, which implies any catcher is likely not going to free the string. So I need some other place to store the result, but where would that be? (I need thread-safety.)

• what also includes throw() in its signature. While I can prevent my what from throwing anything, it seems to me that this method really isn't intended for anything too dynamic. If what is not the right place, then where should I be doing this instead?