Question

From cplusplus.com std::sort complexity is defined:

Complexity

Approximately N*logN comparisons on average (where N is last-first).
In the worst case, up to N2, depending on specific sorting algorithm used by library implementation.

I have some limitations at running time for my apps. So i need to know if should i implement my own sorting algorithm or it would be only waste of time. They are compiled with gcc, so i need to know which sorting algorithm gcc uses.

Answer 1

GCC uses a variation of Musser’s introsort. This guarantees a worst-case running time of O(n log n):

It begins with quicksort and switches to heapsort when the recursion depth exceeds a level based on … the number of elements being sorted.

The implementation can be found in the stl_algo.h header in the __introsort_loop function.