Can CPP preprocessing statement in Fortran be indented?

Question

I am fairly new to use Fortran preprocessing statement and have a question which is probably pretty native. Can Fortran preprocessing statement be indented? I tested using G

Answer 1

No, they cannot be indented because gfortran runs CPP in traditional mode which does not allow indentation. They must always start in the first column.

You could run CPP manually, but be very very careful about that. If you use the // string concatenation operator somewhere the preprocessor would treat it as a comment. You must use the -C flag as shown by @ewcz in his/her answer which disables discarding of comments.

Some compilers supply their own FPP preprocessor which behaves differently.

Answer 2

you could use the C preprocessor to do the processing and then compile the processed file, i.e., assuming that your program is in main.f90, then something like:

cpp -nostdinc -C -P -w main.f90 > _main.f90
gfortran -o main _main.f90

In this connection, this question is quite useful: Indenting #defines