ATL::CStringW vs. std::wstring Performance: String Sorting and Comparisons

According to previous measurements, std::wstring performs better than ATL::CStringW:

  1. in all string concatenation tests
  2. when sorting string vectors that are made by small strings, thanks to std::basic_string’s SSO

So, I focused my attention on the string vector sorting scenario, and it seems to me that (at least in the VS2015 implementation), the slowdown of (non-SSO) wstrings is caused by wmemcmp calls, that are used to compare wstrings when sorting the string vectors. On the other hand, CStringW invokes wcscmp, that seems to run faster.

In fact, invoking std::sort with a custom comparator function that calls wcscmp to compare the C-style pointers returned by wstring::c_str, results in faster vector<wstring> sorting times. So, in this case wstring sorting performs better than CStringW even for non-SSO strings.

However, as Stephan T. Lavavej pointed out, std::basic_string supports embedded nulls, so wstring cannot use wcscmp (that works only for C-style null-terminated strings, without embedded nulls).

 

String Performance Tests: ATL vs. STL

I wrote some C++ code to test the performance of the ATL CStringW class vs. the C++ Standard Library’s std::wstring.

There are several aspects that can be considered when comparing string class performance: In the aforementioned code, I tested string vector sorting and string concatenation.

The code is available in this repository on GitHub.

You can take a look at the README for further details (including my test results).

 

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