How much extra memory (if any) does a std::set take to store its elements v.s. a std::vector?

Question

It must be implementation dependent, but is there any sort of significant memory overhead to using std::set ?

EDIT: In my case, I have a set of std::string, with average string length of 9 letters.

Answer 1

A std::set is implemented as a binary tree, so has nodes with left and right pointers as well as a data element. The allocation for each of these may be rounded up by your dynamic memory library functions. So yes - for elements of a machine word or three, the overhead's going to be "significant" as a ratio/percentage (eg 2 64-bit pointers + a char could easily round up to eg 32 bytes... a 32x overhead), and may or may not be significant from an system/application behaviour perspective. If you care, always measure on your own system.

For average-9-char string s, overall memory usage will be not only a factor of whether you use set or vector , but also how many string 's text will fit into any Short-String-Optimisation buffer (internal to the string object; if you implementation provides such an optimisation), rather than needing further dynamic memory allocated to store the text.