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

I don't think there's a big performance gain if you choose pointer instead of object. Only do this if you're managing data with lot of existing string objects which need to hold inside the container. Also the destruction of the objects has to be managed manually before destructing the container.