Linking to modules folder gives undefined reference

Question

if I understood the manual correctly it should work to creat a file containing a fortran module in a folder, say /path/mods/test_mod.f90 i.e. :

module test_mod
i         


        

Answer 1

You need to include the .o file as well. That is, you should compile this as

gfortran -I/path/to/mods -o test_prog test_prog.f90 mods/test_mod.o

This worked and ran for me.

Answer 2

This

gfortran -c test_mod.f90

should produce two files: test_mod.mod and test_mod.o. Your other compilation statement

gfortran -I/path/mods -o test_prog test_prog.f90

correctly specifies the location in which to look for the .mod file but omits the .o file. The .mod file is a bit like a compiler-generated header file, it is used for compilation of any program units which use-associate the module, but the object file is needed for linking.

The simplest (I think) fix is to write

gfortran -o test_prog -I/path/mods /path/mods/test_mod.o test_prog.f90

but you may want to fiddle around with that.