Wsrtjtyk

I have the following class declaration -

template <typename T> 

class Polynomial{

  std::map<std::string, T> _polynomial_

}

In a member function I declared an iterator for this -

typename std::map<std::string, T>::iterator it= _polynomial_.begin();

The completed member function looks like this -

template <typename T>

void Polynomial<T>::print(std::ostream& out) const

{





  typename std::map<std::string, T>::iterator it= _polynomial_.begin();

  std::string term;

  while(it != _polynomial_.end()){





    term = it->second;

    term += it->first;

    if(it->first < (T)0){

      out << "-" << term;

    }

    else{

      out << "+" << term;

    }

    term = "";

    it++;

  }





}

In main, I call the function as follows -

 Polynomial <double> p1;



  p1.add_term("x0",9.862);



  std::cout << p1;

However this does not seem to work and I get errors. GCC complains of a
conversion error -

Polynomial.hpp:32:47: error: conversion from u2018std::map, double, std::less >, std::allocator, double> > >::const_iterator {aka std::_Rb_tree_const_iterator, double> >}u2019 to non-scalar type u2018std::map, double, std::less >, std::allocator, double> > >::iterator {aka std::_Rb_tree_iterator, double> >}u2019 requested
typename std::map::iterator it= polynomial.begin();

Can someone tell me what is the correct declaration of the iterator?

Polynomial<T>::print is a const member function, inside which the data member _polynomial_ becomes const too, that means what _polynomial_.begin() returns is a const_iterator, which can't be converted to iterator implicitly. (Note that std::map::begin is overloaded with const version and non-const version, the former returns const_iterator and the latter returns iterator.)

Change the code to

typename std::map<std::string, T>::const_iterator it = _polynomial_.begin();

//                                 ^^^^^^

or use auto instead, it would deduce the correct type for you.

auto it = _polynomial_.begin();