preprocessor will include whatever file you specify in your #include
statement. Therefore, if you have the line
in your program, the file macros.inc will be included in your
precompiled program. It is, however, unusual programming practice to
put any file that does not have a .h or .hpp extension in an
You should always put a .h extension on any of your C files you are
going to include. This method makes it easier for you and others to
identify which files are being used for preprocessing purposes.
For instance, someone modifying or debugging your program might not
know to look at the macros.inc file for macro definitions. That
person might try in vain by searching all files with .h extensions
and come up empty.
If your file had been named macros.h, the search would have included
the macros.h file, and the searcher would have been able to see what
macros you defined in it.