C++使用宏来判断当前编译期支持的C++标准版本的方法

     需要注意的是，很多时候，某个编译器的版本并不完整支持某个C++标准，比如Visual Studio 2010 SP1，虽然支持了部分C++ 11的能力，但是依然有很多C++ 11的特性是不支持的。因此单纯通过C++标准的版本号来鉴别C++特性是否可用是并不完备的方法。具体支持情况可以参考这里。

#ifdef _MSC_VER
#define FL_COMPILER_MSVC      1
#else
#define FL_COMPILER_MSVC      0
#endif

#ifdef __GNUC__
#define FL_COMPILER_GCC       1
#else
#define FL_COMPILER_GCC       0
#endif // __GNUC__  // NOLINT

#if FL_COMPILER_MSVC
// @reference https://www.cnblogs.com/bodong/p/18293350
// Each version of Visual Studio does not have complete support for the C++ standard,
// so simply judging the feature support of the C++ standard through these version numbers is incomplete.
#if _MSC_FULL_VER <= 150030729 // before Visual Studio 2008 sp1, set C++ 98
#define _MSVC_LANG 199711
#elif _MSC_FULL_VER <= 180021114 // before Visual Studio 2013 Nobemver CTP, set C++ 11
#define _MSVC_LANG 201103
#elif _MSC_FULL_VER <= 190023918 // before Visual Studio 2015 Update 2, set C++ 14
#define _MSVC_LANG 201402
#endif // after Visual Studio 2015 Update 3, _MSVC_LANG exists

#define FL_COMPILER_LANG_VERSION _MSVC_LANG
#elif defined(__cplusplus)
#define FL_COMPILER_LANG_VERSION __cplusplus
#else // set C++ 98 as default
#define FL_COMPILER_LANG_VERSION 199711
#pragma message("No valid C++ standard identification flag found, default to C++98 standard")
#endif

// is greater than ?
// Checks whether the current C++ standard is a later version
#define FL_COMPILER_IS_GREATER_THAN_CXX23 (FL_COMPILER_LANG_VERSION >= 202101)
#define FL_COMPILER_IS_GREATER_THAN_CXX20 (FL_COMPILER_LANG_VERSION >= 202002)
#define FL_COMPILER_IS_GREATER_THAN_CXX17 (FL_COMPILER_LANG_VERSION >= 201703)
#define FL_COMPILER_IS_GREATER_THAN_CXX14 (FL_COMPILER_LANG_VERSION >= 201402)
#define FL_COMPILER_IS_GREATER_THAN_CXX11 (FL_COMPILER_LANG_VERSION >= 201103)
#define FL_COMPILER_IS_GREATER_TAHN_CXX98 (FL_COMPILER_LANG_VERSION >= 199711)

// is C++ xx ?
// Check whether the current C++ standard specifies a certain version
#define FL_COMPILER_IS_CXX23 (FL_COMPILER_LANG_VERSION >= 202101)
#define FL_COMPILER_IS_CXX20 (FL_COMPILER_LANG_VERSION >= 202002 && FL_COMPILER_LANG_VERSION < 202101)
#define FL_COMPILER_IS_CXX17 (FL_COMPILER_LANG_VERSION >= 201703 && FL_COMPILER_LANG_VERSION < 202002)
#define FL_COMPILER_IS_CXX14 (FL_COMPILER_LANG_VERSION >= 201402 && FL_COMPILER_LANG_VERSION < 201703)
#define FL_COMPILER_IS_CXX11 (FL_COMPILER_LANG_VERSION >= 201103 && FL_COMPILER_LANG_VERSION < 201402)
#define FL_COMPILER_IS_CXX98 (FL_COMPILER_LANG_VERSION >= 199711 && FL_COMPILER_LANG_VERSION < 201103)

       可以简单测试一下：

#if FL_COMPILER_IS_CXX23
#pragma message("C++ 23")
#elif FL_COMPILER_IS_CXX20
#pragma message("C++ 20")
#elif FL_COMPILER_IS_CXX17
#pragma message("C++ 17")
#elif FL_COMPILER_IS_CXX14
#pragma message("C++ 14")
#elif FL_COMPILER_IS_CXX11
#pragma message("C++ 11")
#elif FL_COMPILER_IS_CXX98
#pragma message("C++ 98")
#else
#error "can't find C++ compiler version."
#endif