Intel XENIX 286 Programmers Guide (86) - Tenox.tc

XENIX Programming cc: C Compiler
You may use -D to define up to 20 macros on a command line. However, you cannot
redefine a macro once it has been defined. If a file uses a macro, you must place the -D
option before that file's name on the command line. For example, in the command
cc main.c -DNEED a dd.c
the macro "NEED" is defined for add.c but not defined for main.c.
The -U option undefies a macro defined by a #define in each source file. The form -D
name sets name to 0. The form -U name = string redefines name as the given string.
Defining Include Directories
You can explicitly define directories containing "include" files by using the -1 (for
"include") option. This option adds the given directory to a list of directories to be
searched for include files. The directories in the list are searched whenever an include
directive is encountered in the source file. The option has the form
-Idirectoryname
where directoryname is a valid path name to a directory containing include files. For
example, the command
cc -1/usr/joe/include main.c
causes the compiler to search the directory /usr/joe/include for include files requested
by the source file main.c.
The directories are searched in the order they are listed and only until the given include
file is found. The /usr/include directory is the default include directory and is
automatically searched after directories given with -1.
Ignoring the Default Include Directories
You can prevent the C preprocessor from searching the default include directory by
using the -X option. This option is generally used with the -1 option to define the
location of include files that have the same names as those found in the default
directories, but which contain different definitions. For example, the command
cc -X -1/usr/joe/include main.c add.c
causes cc to look for all include files only in the directory /usr/joe/include.
2-13