There options affect how affect how gfortran searches
for files specified via the
INCLUDE directive, and where it searches
for previously compiled modules.
It also affects the search paths used by cpp when used to preprocess Fortran source.
INCLUDEdirective (as well as of the
#includedirective of the cpp preprocessor).
Also note that the general behavior of -I and
INCLUDE is pretty much the same as of -I with
#include in the cpp preprocessor, with regard to
looking for header.gcc files and other such things.
This path is also used to search for `.mod' files when previously
compiled modules are required by a
See Options for Directory Search, for information on the -I option.
The default is the current directory.
-J is an alias for -M to avoid conflicts with existing GCC options.