一次使用时，出现报错：

warning: exception of type ‘std::bad_alloc’ will be caught
 catch (bad_alloc e){ cout << e.what() << endl;}
 ^~~~~
 
warning:    by earlier handler for ‘std::exception’
 catch (exception e){ cout <<  e.what() << endl;}

catch语句块不能随意乱安排。派生类型的异常放在前面，基类异常应该放在最后

int main()
{  
    try {  
        throw DerivedException();  
    }
    catch (DerivedException& e) { // Handle derived class first  
        std::cerr << "Caught DerivedException: " << e.what() << std::endl;  
    }
    catch (BaseException& e) { // Then handle base class  
        std::cerr << "Caught BaseException: " << e.what() << std::endl;  
    }  
    return 0;  
}

catch(...) 是一个通配符，能够捕获任何未被其他 catch 块处理的异常。避免滥用 catch(...)，尽量捕获特定类型的异常，避免掩盖问题。