C++ return intermediate reference

Asked Feb 04 '17 at 22:35

Active Feb 04 '17 at 22:35

Viewed 61 times

I have a 2d version of valarray called matrix. I want to access one column of it and use it as the left value outside of the class. The IDE gives me the following error on the return line. I guess [] operator of valarray returns an intermediate array and should be used immediately? How to fix this? Thank you

Non-const lvalue reference to type 'slice_array<[...]>' cannot bind to a temporary of type'slice_array<[...]>'

class matrix
{
public:
    matrix(int rows, int columns): _rows(rows), _columns(columns),storage(rows*columns) {}
    // Access a column
    slice_array<double> &operator()(int c){
        return storage[slice(c,_row,_columns)];
    }
private:
    int _rows;
    int _columns;
    valarray<double> storage;

asked Feb 04 '17 at 22:35

Chris Zhang

Where is your [MCVE]? – Lightness Races in Orbit Feb 04 '17 at 22:48
_"use it as the left value outside of the class"_ What does this mean? – Lightness Races in Orbit Feb 04 '17 at 22:50
Well, that `[]` returns a `slice_array`, because that's what you asked it to do ([ref](http://en.cppreference.com/w/cpp/numeric/valarray/operator_at)). And now you're trying to return a reference to that temporary. That doesn't make sense. Did you mean to return by value? N.B. `slice_array` itself has reference semantics, if that's what you're worried about... – Lightness Races in Orbit Feb 04 '17 at 22:51

C++ return intermediate reference

0 Answers0