why is c++ std::max_element so slow?

Question

I need to find the max element in the vector so I\'m using std::max_element, but I\'ve found that it\'s a very slow function, so I wrote my own version and manage t

Answer 1

You are probably running your test in 64-bit mode, where sizeof(int) == 4, but sizeof(std::vector<>::iterator) == 8, so that assignment in the loop to int (what my_max_element does) is faster than to std::vector<>::iterator (this is what std::max_element does).

If you change std::vector to std::vector results change in favour to std::max_element:

MaxIter = 1000000012
MaxArray = 1000000012
Total CPU time iterator = 0.00429082
Total CPU time array = 0.00572205
iter/array ratio: = 0.749875

One important note: when benchmarking disable the CPU frequency scaling, so that the CPU does not switch gears in the middle of the benchmark.

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But I think something else is at play here, since just changing the loop variable from int to long does not change the results...