__cplusplus in MSVC is always 199711L

[Leopard20]

Hi. I recently realized that MSVC always sets __cplusplus to 199711L unless /Zc:__cplusplus is enabled:
https://docs.microsoft.com/en-us/cpp/build/reference/zc-cplusplus?view=msvc-160&viewFallbackFrom=vs-2017

Since you use this macro in your code, I figured I should ask whether it matters in terms of performance:

robin-hood-hashing/src/include/robin_hood.h

Line 51 in 9dbc277

#if __cplusplus >= 201703L

robin-hood-hashing/src/include/robin_hood.h

Line 216 in 9dbc277

#define ROBIN_HOOD_PRIVATE_DEFINITION_CXX() __cplusplus

For now I just replaced the macro with a custom macro I wrote myself so that it uses the latest compiler features.

[martinus]

This only enables the ability to use std::string_view as key in a hashmap. So it's not a performance issue but one feature could be disabled

[harayuu9]

Hi. I think it is better to use __cplusplus and _MSVC_LANG together in MSVC environment.
(This is only available in Visual Studio 2015 or later, but _MSVC_LANG returns the correct value in the standard configuration.

https://docs.microsoft.com/en-us/cpp/preprocessor/predefined-macros?view=msvc-170