3.6.7.5 Imacros Option

The -imacros file option processes the specified file in the same way the -include option would, except that any output produced by scanning the file is thrown away. The macros that the file defines remain defined during processing. Because the output generated from the file is discarded, the only effect of this option is to make the macros defined in file available for use in the main input.

Any -D and -U options on the command line are always processed before an -imacros option, regardless of the order in which they are placed. All the -include and -imacros options are processed in the order in which they are written.