![]() If you have been reading my articles over the years, you will notice they are usually performance-focused. You are welcome to build and run the benchmark with GCC and Clang. What about GCC and Clang? I do not have access to the latest C++ compilers on Linux. Trans Unord Map with string_view timing: 762ms Trans Unord Map with char* timing: 1506ms Normal Unord Map with char* timing: 2382ms Normal Unord Map with string timing: 738ms It should be a bug which I shall report to Microsoft. string_view has about the same performance as std::string that looks about right while const char* has worse performance in transparent map than normal map. Short text should be faster since std::string is implemented with Short String Optimization(SSO), meaning std::string has a short buffer that is used whenever the text is short enough to fit in that buffer, instead of allocating on the heap. ![]() ![]() The benchmark is built in Release 圆4 mode with /Ox, the highest compiler optimization. Std::cout < < " grandtotal:" < < grandtotal < < " <- Ignore this\n" < < std::endl įirst, we run the benchmark with short text. Stopwatch.start( " Trans Unord Map with string_view") Stopwatch.start( " Trans Unord Map with char*") Stopwatch.start( " Normal Unord Map with char*") Stopwatch.start( " Normal Unord Map with string") Stopwatch.start( " Trans Map with string_view") Stopwatch.start( " Trans Map with char*") Stopwatch.start( " Normal Map with char*") Stopwatch.start( " Normal Map with string") Initially, I was using the associative container's operator for search but it turns out that does not accept string_view, so find() is used.Ĭonst std::unordered_map & unordmapNormal,Ĭonst std::unordered_map & unordmapTrans) Their only purpose is to prevent the compiler from optimizing away the for loops since they are not doing any useful work. Ignore the total and grandtotal variables. UnordmapTrans.find( " Terry"sv) // no memory alloc UnordmapTrans.find( " Terry") // no memory alloc but strlen() is used Size_t operator()( std::string_view txt) const Using hash_type = std::hash // just a helper local type ![]() Using key_equal = std::equal_to // Pred to use Care must be taken with accessing string_view that the original std::string or character buffer, it pointed to, must be still in scope. What is a string_view? string_view is a non-owning view to a not-null-terminating character buffer with its length. To help you understand the sv suffix in the later code, it has to be noted whenever sv is appended to a string literal, we are telling the compiler to create a string_view from literal. Thanks, Billy O'Neal and VC++ team! In order to enable the latest C++ standard in VC++ to compile this benchmark, go to VC++ general property page and choose std:c++latest from the C++ Language Standard dropdown as shown below: However, Visual C++ team has already implemented some of C++20 library features. We are officially in 2020 but as of writing time, the C++20 Standard is yet to be ratified by C++ committee. C++20 introduced unordered transparency lookup that allows to do the same thing with unordered_map/unordered_set. Download cpp_hetero_lookup_bench-master_2.zip - 8.8 KBĬ++14 introduced ordered transparency lookup which enables const char* and string_view lookup without string instantiation on map/set objects.
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