Set::find() not working as expected with objects stored as pointer and comparison functor defined

If my set::find() function works as expected in some scenarios and does not work in others.

Since I am storing object pointers in my set I have defined a functor for comparison as below:

template<class T> struct ptr_compare
{
    bool operator()(const T* lhs, const T* rhs) const
    {
        return *lhs < *rhs;
    }
};

My sample class is as below:

class A {
  private:
    string str;
  public:
    A(string s)
    {
        str = s;
    }
    bool operator <(const A& obj) const
    {
        return this->str.compare(obj.get_str());
    }
    
    string get_str() const
    {
        return str;
    }
};

If I write main() function as below then set::find() seem to work as expected:

int main()
{
    set<A*, ptr_compare<A>> myset;
    A* a1 = new A("sdkbf");
    A* a2 = new A("test");
    A* a3 = new A("sfj");
    
    myset.insert(a1);
    myset.insert(a2);
    myset.insert(a3);
    
    set<A*>::iterator it = myset.find(a2);
    if (it != myset.end())
    {
        cout << "found" << endl;
    }
    else
    {
        cout << "not found" << endl;
    }

    return 0;
}

Output of above: found

Now If I change the order in which I insert elements in set then set::find() does not work as expected:

int main()
{
    set<A*, ptr_compare<A>> myset;
    A* a1 = new A("sdkbf");
    A* a2 = new A("test");
    A* a3 = new A("sfj");
    
    myset.insert(a1);
    myset.insert(a3);
    myset.insert(a2);
    
    set<A*>::iterator it = myset.find(a2);
    if (it != myset.end())
    {
        cout << "found" << endl;
    }
    else
    {
        cout << "not found" << endl;
    }

    return 0;
}

Output of above: not found

Is this not right way to compare object pointers in a set.

>Solution :

The issue is with

bool operator <(const A& obj) const
{
    return this->str.compare(obj.get_str());
}

Here compare will return -1 if str is less than obj.get_str() and 1 if obj.get_str() is less than str. Both of those values get converted to true when returned as a bool from the function. This is not what you want. Instead, you can use std::strings operator < like

bool operator <(const A& obj) const
{
    return str < obj.str;
}