3.2.2 Using Custom Preprocessor

The default preprocessor can be changed (or even disabled) at compile time as well as on the runtime. When invoked with the --help option pies reports, among others, the preprocessor it is configured to use and the default include search path.

To disable preprocessing, use the --no-preprocessor command line option.

To change the default preprocessor at runtime, use the --preprocessor option. Its argument is the initial preprocessor command line. Depending on the pies command line, it can be further modified by appending new options as described in additional preprocessor options.

When selecting another preprocessor, please bear in mind that pies assumes that the preprocessor program understands the following three options:

-D name[=value]

Define the preprocessor symbol name.

-I dir

Add the directory dir to the preprocessor search path for include files.

-U name

Undefine the preprocessor symbol name.

pies never passes -D and -U options, except as if these were passed to it in the command line.

However, it normally adds one or more -I options to configure the default search path.

If the preprocessor of your choice doesn’t support some or any of these options, there are several possible solutions.

• If the preprocessor doesn’t support -D and -U options, don’t pass them in the pies command line.
• If it does not support the -I option, run pies with the --no-include option or create a wrapper script which will consume all -I options without affecting the preprocessor command line.

For an example of using alternative preprocessor, See xenv.