Which sorting algorithm is used in GCC?

Question

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

Complexity

Approximately N*logN comparisons on average (where N is last

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.