Question

struct Set
{
    int a;
    Set() : a(30){};
    bool operator>( const Set& ref ) const
    {
        return ref.a > this->a;
    };
};

int _tmain(int argc, _TCHAR* argv[])
{   
    vector<Set>m_set;
    m_set.push_back( (*(new Set)) );
    cout << m_set.at(0).a;
    delete &(m_set.at(0));
    if( &(m_set.at(0).a) )
        cout << "valid" << endl;

    return 0;
}

Why does it outputs valid, is deleting using this method invalid?

Answer 1

When you access an object that has been deleted the behavior is undefined. Anything can happen.

EDIT: and, more to the point, when you delete an object that wasn’t created with new, the behavior is undefined. Anything can happen. That’s what the code here does.