Test the C/C++ standard version

standard_test.cpp

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#if defined __cplusplus /* [ */
#if   __cplusplus == 1  /* [ */
#error "pre-standard C++"
#elif __cplusplus == 199711L
#error "C++ 98 or C++03"
#elif __cplusplus > 199711L && __cplusplus < 201103L
#error "C++ 0x"
#elif __cplusplus == 201103L
#error "C++ 11"
#elif __cplusplus > 201103L && __cplusplus < 201402L
#error "C++ 1y"
#elif __cplusplus == 201402L
#error "C++ 14"
#elif __cplusplus == 201703L
#error "C++ 17"
#elif __cplusplus > 201703L
#error "C++ 2a"
#else
#error "unknown C++ version"
#endif               /* __cplusplus ] */
#elif   defined __STDC__ /* __cplusplus ] [  */
#if   defined __STDC_VERSION__ /* [ */
#if   __STDC_VERSION__ == 199409L /* [ */
#error "C 94"
#elif __STDC_VERSION__ == 199901L
#error "C 99"
#elif __STDC_VERSION__ == 201112L
#error "C 11"
#elif __STDC_VERSION__ == 201710L
#error "C 18"
#else
#error "unknown C version"
#endif /* __STDC_VERSION__ ] */
#else
#error "C 89"
#endif /* __STDC_VERSION__ ] [ */
#endif /* __STDC__ ] */