当构造函数抛出异常时，构造函数中分配的内存是如何释放的？

Question

Below is my sample code. Base class has a pointer of A class with memory assigned from heap using new operator. I am explicitly throwing an exception. Since I am not invoking delete on *ptr the memory allocated by new is not released. Since the object is not constructed completely how can we release memory?

#include <iostream>

using namespace std;
class A
{
    public:
    A()
    {
        cout<<"A::ctor"<<endl;
    }
    ~A()
    {
        cout<<"A::Dctor"<<endl;
    }
};
class Base
{
    public:
    A *ptr;
    Base()
    {
       ptr = new A();
        cout<<"Base::Ctor"<<endl;
        throw std::exception();
    }
    ~Base()
    {
        delete ptr;
        cout<<"Base::Dtor"<<endl;
    }
};

int main()
{
    try{
        Base bobj;

    }
    catch(exception e)
    {

        cout<<e.what();
    }

    return 0;
}

When Base constructor throws exception the control goes to catch block and exception is handled. But how is the memory allocated by ptr = new A(); released?

Now I know using smart pointers would solve the issue. But before C++11 how were such situations handled.

In addition, I would like to know how do we close file handlers of a file handler is opened in constructor and constructor has an exception?

Base()
{
 ofstream myfile;
 myfile.open("myfile.txt");
 ..........
 throw std::exception();
}

~Base()
{
  myfile.close();
}

Answer 1

The memory associated with ptr is never released!

Yes, that was always a problem.

Prior to C++11 you could build your own smart pointer class (or use the one in Boost for example), or take care to delete prior to throwing an exception. Putting ptr in a base class is also an alternative: the base class constructor will complete before the derived constructor's function body is reached.