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

C++11

Since C++11 reference wrapper is part of standard.

#include  

std::map, data>

Using Boost

You may want to take a look at boost.ref. It provides a wrapper that enables references to be used in STL-containers like this:

std::map, data>