C language preprocessing command #error learning

The #error command is one of the preprocessing commands of the C/C++ language. When the preprocessor preprocesses to the #error command, it will stop compiling and output a user-defined error message.

The following code outputs the number 1000. If #error is added, the build will not pass, and the error message is as follows;

This may be useful in larger projects; 

The following is said to be an example in the freertos source code, 

#ifndef configEXPECTED_IDLE_TIME_BEFORE_SLEEP
    #define configEXPECTED_IDLE_TIME_BEFORE_SLEEP 2
#endif
 
#if configEXPECTED_IDLE_TIME_BEFORE_SLEEP < 2
    #error configEXPECTED_IDLE_TIME_BEFORE_SLEEP must not be less than 2
#endif
如果configEXPECTED_IDLE_TIME_BEFORE_SLEEP  定义的小于2，则编译出错；