8.3.2.2 Symbols

• -D
  • -Dname

    Predefine name as a macro, with definition 1.

  • -Dname=value

    Predefine name as a macro, with definition value. The contents of the definition are tokenized and processed as if they appeared during translation phase three in a #define directive. In particular, the definition will be truncated by embedded newline characters.

• -U

  Cancel any previous name definition, either built-in or provided with a -D option.

-D and -U options are processed in the order given on the command-line. All -imacros file and -include file options are processed after all -D and -U options.