Diagnostics

5 Diagnostics

The directive ‘#error’ causes the preprocessor to report a fatal error. The tokens forming the rest of the line following ‘#error’ are used as the error message.

You would use ‘#error’ inside of a conditional that detects a combination of parameters which you know the program does not properly support. For example, if you know that the program will not run properly on a VAX, you might write

#ifdef __vax__
#error "Won't work on VAXen.  See comments at get_last_object."
#endif

If you have several configuration parameters that must be set up by the installation in a consistent way, you can use conditionals to detect an inconsistency and report it with ‘#error’. For example,

#if !defined(FOO) && defined(BAR)
#error "BAR requires FOO."
#endif

The directive ‘#warning’ is lik