Question

I can’t understand why the following code is not working, any idea ?

template <class T>
class Matrice
{
public:
...
    typedef typename std::vector<T>::const_iterator const_iterator;
    const_iterator& cend ( )
    {
        return valeurs.cend ( );
    }
...
private:
...
}

here’s the complilator’s complaint :

/Users/Aleks/Documents/DS OO/DS OO/Matrice.h:70:16: Non-const lvalue
reference to type ‘const_iterator’ (aka ‘__wrap_iter’)
cannot bind to a temporary of type ‘const_iterator’ (aka
‘__wrap_iter’)

Answer 1

valeurs.cend (cppreference) returns an instance to a const_iterator (that is, it’s declared as const_iterator valeurs.cend()).

The compiler needs to create a temporary object (memory area) to store the value returned by valeurs.cend(). This code fails to compile because you cannot take the reference of a temporary as the latter won’t outlive the function call.

You’d usually return an iterator by value:

typedef typename std::vector<T>::const_iterator const_iterator;
const_iterator cend ( )
{
    return valeurs.cend ( );
}

This will make sure the value returned by valeurs.cend() is copied (or moved, in C++11, I believe) to its the destination object (if you’re assigning the returned value to a variable of type const_iterator) or in another temporary wherever Matrice<T>::cend() is called. See the link to MSDN’s explanation for details.