return reference to temporary when dereferencing map iterator

Question

Consider this code

#include 
#include 

const int& foo(const std::vector& x,unsigned i) {
    auto it = x.be         


        

Answer 1

The problem is that the value_type of std::map is not std::pair, but std::pair. Then for return *it;, a temporary std::pair has to be created and returned. (std::pair could be converted from std::pair.) The temporary will be destroyed immediately and left the returned reference dangled.

To sovle the issue you can change the return type to const std::pair& or const std::map::value_type &.