|#error directive||Issues an error message|
The #error directive tells the preprocessor to issue an error message and mark the source file as ill-formed, just as if the programmer made a programming error that the compiler detected. You can supply any sequence of preprocessor tokens as the message, and those tokens are echoed in the error message.
#if !defined(_ _cplusplus) || (_ _cplusplus < 199711L) #error Not a conforming C++ compiler. #endif