+ The standard exception classes carry with them a single string as + data (usually describing what went wrong or where the 'throw' took + place). It's good to remember that you can add your own data to + these exceptions when extending the hierarchy: +
+ struct My_Exception : public std::runtime_error
+ {
+ public:
+ My_Exception (const string& whatarg)
+ : std::runtime_error(whatarg), e(errno), id(GetDataBaseID()) { }
+ int errno_at_time_of_throw() const { return e; }
+ DBID id_of_thing_that_threw() const { return id; }
+ protected:
+ int e;
+ DBID id; // some user-defined type
+ };
+