Using Module (.mod) Files

One way to reduce potential confusion when you use the same source code in several projects is to organize the routines into modules. A module (.mod file) is a type of program unit that contains specifications of such entities as data objects, parameters, structures, procedures, and operators. These precompiled specifications and definitions can be used by one or more program units. Partial or complete access to the module entities is provided by the program's USE statement. Typical applications of modules are the specification of global data or the specification of a derived type and its associated operations.

Modules are excellent ways to organize programs. You can set up separate modules for:

• Commonly used routines.

• Data definitions specific to certain operating systems.

• System-dependent language extensions.

Some programs require modules located in multiple directories. You can use the I compiler option when you compile the program to specify the location of the .mod files that should be included in the program.

You can use the modulepath compiler option to specify the directory in which to create the module files. If you do not use this option, module files are created in the current directory.

Directories are searched for .mod files in this order:

1. Directory of the source file that contains the USE statement.

2. Directories specified by the modulepath compiler option.

3. Current working directory.

4. Directories specified by the -Idir (Linux* and OS X*) or /include (Windows*) option.

5. Directories specified with the CPATH or INCLUDE environment variable.

6. Standard system directories.

You need to make sure that the module files are created before they are referenced by another program or subprogram.

module test
integer:: a
contains
  subroutine f()
  end subroutine
end module test 
module payroll 
  ...
end module payroll 

ifort -ca.f90

file: mod_def.f90
module definedmod
  ...
end module

ifort -c mod_def.f90

file: use_mod_def.f90
program usemod
use definedmod 
  ...
end program