21. The need for a copy constructor

// This program crashes:
class Terminator {
    int* m_ptr;
public:
    Terminator( int* ptr )
    {
        m_ptr = ptr;
    }

    ~Terminator()
    {
        delete m_ptr;
    }
};//class Terminator

int main()
{
    int* ptr = new int;
    *ptr = 12345;
    Terminator alice( ptr );
    Terminator bob = alice;
    return 0;
}

// Solution:
class Terminator {
    int* m_ptr;
public:
    Terminator( int* ptr )
    {
        m_ptr = ptr;
    }

    // Copy constructor -- deep copy
    Terminator( Terminator& another )
    {
        m_ptr = new int;
        if ( another.m_ptr ) {
            *m_ptr = *another.m_ptr;
        }
    }

    ~Terminator()
    {
        delete m_ptr;
    }
};//class Terminator