The #error directive

A preprocessor error directive causes the preprocessor to generate an error message and causes the compilation to fail.

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#error directive syntax

             .--------------------.   
             V                    |   
>>-#--error----preprocessor_token-+----------------------------><

The #error directive is often used in the #else portion of a #if#elif#else construct, as a safety check during compilation. For example, #error directives in the source file can prevent code generation if a section of the program is reached that should be bypassed.

For example, the directive
#define BUFFER_SIZE 255

#if BUFFER_SIZE < 256
#error "BUFFER_SIZE is too small."
#endif
generates the error message:
BUFFER_SIZE is too small.