C++ runtime, display exception message

You could write in main:

try{

}catch(const std::exception &e){
   std::cerr << e.what() << std::endl;
   throw;
}

You could use try/catch block and throw; statement to let library user to handle the exception. throw; statement passes control to another handler for the same exception.

Standard exceptions have a virtual what() method that gives you the message associated with the exception:

int main() {
   try {
       // your stuff
   }
   catch( const std::exception & ex ) {
       cerr << ex.what() << endl;
   }
}