Problem while compoiling

[MohammadMirsafaei]

Hi
I was trying to compile ncorr on visual studio 2019.
But there is an error in code!
How can I fix it?
Threre are several places in code with this issue

template <typename T_container> 
    inline typename sub_iterator<T_container>::sub_iterator& sub_iterator<T_container>::operator++() {    
        this->chk_valid_increment();

        // increment sub_p, then determine position from it
        ++sub_p;
        this->p = this->A_ptr->sub2ind(sub_p % sub_h + r_sub1_2D.first, sub_p / sub_h + r_sub2_2D.first);

        return *this;
    }  

and the error is :
overloaded function "ncorr::details::sub_iterator<T_container>::sub_iterator" is not a type name