Consider the following code:

class CString
{
private:
    char* buff;
    size_t len;

public:
    CString(const char* p):len(0), buff(nullptr)
    {
        cout << "Constructor called!"<<endl;
        if (p!=nullptr)
        {
            len= strlen(p);
            if (len>0)
            {
                buff= new char[len+1];
                strcpy_s(buff, len+1, p);               
            }           
        }       
    }

    CString (const CString& s)
    {
        cout << "Copy constructor called!"<<endl;
        len= s.len;
        buff= new char[len+1];
        strcpy_s(buff, len+1, s.buff);      
    }

    CString& operator = (const CString& rhs)
    {
        cout << "Assignment operator called!"<<endl;
        if (this != &rhs)
        {
            len= rhs.len;
            delete[] buff;          
            buff= new char[len+1];
            strcpy_s(buff, len+1, rhs.buff);
        }

        return *this;
    }

    CString operator + (const CString& rhs) const
    {
        cout << "Addition operator called!"<<endl;

        size_t lenght= len+rhs.len+1;
        char* tmp = new char[lenght];
        strcpy_s(tmp, lenght, buff);
        strcat_s(tmp, lenght, rhs.buff);

        return CString(tmp);
    }

    ~CString()
    {
        cout << "Destructor called!"<<endl;
        delete[] buff;
    }     
};

int main()
{
CString s1("Hello");
CString s2("World");
CString s3 = s1+s2;     
}

My problem is that I don't know how to delete the memory allocated in the addition operator function(char* tmp = new char[length]). I couldn't do this in the constructor(I tried delete[] p) because it is also called from the main function with arrays of chars as parameters which are not allocated on the heap...How can I get around this? (Sorry for my bad English...)