The diagnostic directives are used to explicitly generate error and warning messages that are reported in the same way as other compile-time errors and warnings.

pp-diagnostic

whitespace_opt # whitespace_opt error pp-message

whitespace_opt # whitespace_opt warning pp-message

pp-message

new-line

whitespace input-characters_opt new-line

[Example: The example

#warning Code review needed before check-in #if Debug && Retail #error A build can't be both debug and retail #endif class Test {...}

always produces a warning ("Code review needed before check-in"), and produces a compile-time error if the pre-processing identifiers Debug and Retail are both defined. Note that a pp-message can contain arbitrary text; specifically, it need not contain well-formed tokens, as shown by the single quote in the word can't. end example]