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Editorial Team
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Asked: 2026-05-23T12:27:37+00:00

I believe that the C++ standard for std::sort does not guarantee O(n) performance on

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I believe that the C++ standard for std::sort does not guarantee O(n) performance on a list that’s already sorted. But still, I’m wondering whether to your knowledge any implementations of the STL (GCC, MSVC, etc) make the std::is_sorted check before executing the sort algorithm?

Asked another way, what performance can one expect (without guarantees, of course) from running std::sort on a sorted container?

Side note: I posted some benchmarks for GCC 4.5 with C++0x enabled on my blog. Here’s the results:

Comparison of std::sort and std::is_sorted

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1 Answer

  1. Editorial Team

    Implementations are free to use any efficient sorting algorithm they want so this is highly implementation dependant

    However I have seen a performance comparison of libstdc++ as used on linux and against libc++ the new C++ library developed by Apple/LLVM. Both these libraries are very efficient on sorted or reverse sorted data (much faster than on a random list) with the new library being considerable faster then the old and recognizing many more patterns.

    To be certain you should consider doing your own benchmarks.

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