[Detect C or C++ Standard from Predefined Macros] #c #cpp

.Detect C or C++ Standard from Predefined Macros.md

See the following:

• The C Preprocessor Manual, 3.7.1 "Standard Predefined Macros"
• Pre-defined Compiler Macros

C

C Standard	__STDC__	__STDC_VERSION__
C89	1	#undef
C90	1	#undef
C94	1	199409L
C99	1	199901L
C11	1	201112L
C17	1	201710L
C2X, GNU2x	1	strictly larger than 201710L

C++

C++ Standard	__STDC__	__cplusplus	__cplusplus_cli
C++98	1	199711L	#undef
C++11	1	201103L	#undef
C++14	1	201402L	#undef
C++17	1	201703L	#undef
C++2a, GNU++2a	1	strictly larger than 201703L	#undef
C++/CLI		#undef	200406L

version.c

#include <stdio.h>

int main(int argc, char** argv){
    
    switch(__STDC_VERSION__){
        case 199409L: 
            printf("__STDC_VERSION__ %l (C94)\n");
            break;
        case 199901L: 
            printf("__STDC_VERSION__ %l (C99)\n");
            break;
        case 201112L: 
            printf("__STDC_VERSION__ %l (C11)\n");
            break;
        case 201710L:
            printf("__STDC_VERSION__ %l (C17)\n");
            break;
        default:
            printf("__STDC_VERSION__ %l");
            __STDC_VERSION__ > 201710L  ? printf(" (std=c++2a)\n");
                                        : printf(" Unknown standard\n");
            
    }
    return 0;
}

version.cpp

#include <iostream>

int main() {
  switch (__cplusplus) {
  case 199711L:
    std::cout << __cplusplus << " (std=c++98)" << std::endl;
    break;
  case 201103L:
    std::cout << __cplusplus << " (std=c++11)" << std::endl;
    break;
  case 201402L:
    std::cout << __cplusplus << " (std=c++14)" << std::endl;
    break;
  case 201703L:
    std::cout << __cplusplus << " (std=c++17)" << std::endl;
    break;
  default:
    std::cout << __cplusplus;
    __cplusplus > 201703L ? std::cout << " (std=c++2a)" << std::endl
                          : std::cout << " Unknown standard" << std::endl;
  }

  return 0;
}