Reference as key in std::map

Question

Suppose some data structure:

typedef struct {
    std::string s;
    int i;
} data;

If I use the field data.s as key when adding i

Answer 1

You cannot use the reference. The map can copy the content. This is I guess implementation dependent.

But tested with the microsoft STL.

struct data
{
            data(data const& rhs)
            {
               a new object will be created here
            }
            std::string s;
            int i; 
};

Add some objects to the map and you will run into the copy constructor. This should invalidate your reference.