c++ - Returning a reference of an std::list element from its iterator -

new c++, i've been asked make function in matrix class returns reference value in spot (i,j).

as part of assignment, class holds array of std::list represent matrix:

list <value_type> * m_val; 

which doesn't make sense, well, that's assignment. told start working this:

template <class e> inline e& matrix<e>::operator() (unsigned i, unsigned j) {  } 

this tried:

template <class e> inline e& matrix<e>::operator() (unsigned i, unsigned j) {     list<value_type> row = m_val[i];    // row     typename list< e >::iterator = row.begin();  // iterator @ beginning of row     (int x = 0; x < j; ++x) {         ++it; // each column, increase iterator until reach desired spot     }       return *it;   // i'm confused here. got iterator in right spot, not sure how return reference value. } 

but far can tell, returns value, not reference. want achieve essentially

mymatrix(2,3) = 50;   // value @ 2,3 50. 

list <value_type> * m_val;

this doesn't good. if you're using standard containers, why not use std::vector < list<value_type > or std::array < list<value_type> >?

apart that:

template <class e> inline e& matrix<e>::operator() (unsigned i, unsigned j) {     // less error-prone bounds-checking, remy lebeau stated in comment     if(i >= size_of_m_val_array)     {         throw std::out_of_range("first index out of range");     }      //list<value_type> row = m_val[i];    // copy list     list<value_type>& row = m_val[i];      typename list<value_type>::iterator = row.begin();      // less error-prone bounds-checking, remy lebeau stated in comment     if(j >= row.size())     {         throw std::out_of_range("second index out of range");     }      std::advance(it, j);      return *it;   // correct :) `*it` returns `value_type&` } 

bounds-checking isn't mandatory, though - sure document (and point out!) if don't check.

i'd rather use e or value_type consistently.

c++11 one-liner:

template < class e > inline e& matrix<e>::operator() (unsigned i, unsigned j) {     return std::next( m_val[i].begin(), j ); }