What is the difference regarding memory allocation and efficiency between using a struct with two fields and a pair?
std::pair provides pre-written constructors and comparison operators. This also allows them to be stored in containers like std::map without you needing to write, for example, the copy constructor or strict weak ordering via
operator < (such as required by
std::map). If you don't write them you can't make a mistake (remember how strict weak ordering works?) so it's more reliable just to use