quick accessing to element of std::map

Question

Hi all

do you know if it is any difference in performance when I access a std::map element using find or operator []? One returns an iterator and the other a const ref to the object. Which one might be quicker becuase of all of the behind the scene of the STL?

Regards AFG

Answer 1

When you use [] on a key that doesn't exist, the default element will be inserted. This default element depends on your map definition (for example, for an int it will be a zero).

When you use find, there is no "automatic" insertion, so it can be quite faster if you often search for keys that does not exist.

Answer 2

find() is O(n). operator [] is O(1). Therefore the latter is (usually) faster.