Inserting into a map is faster using value_type than std::pair.

Here are four common ways to insert into a map:

std::map m;

• m[0] = 100;
• m.insert(std::pair<int, int>(0, 100));
• m.insert(std::make_pair(0, 100));
• m.insert(std::map<int, int>::value_type(0, 100));

The last one is the fastest. My benchmarks showed that inserting using value_type is 2-5% faster than using pair, depending on optimization flag. I missed this obvious part of C++ because its syntax is more complex than the other solutions. Terrible reason, but there it is.

Also, to state the obvious: m[0] = 100 is not equivalent to an insert. An insert will not overwrite any previous value. Surprised? So was I.

Source: C++ reference: std::map::insert
Quote: "[T]he insertion operation checks whether each inserted element has a key equivalent to the one of an element already in the container, and if so, the element is not inserted, returning an iterator to this existing element"