pablordrrbl/cmake_fortran_template

A template directory structure for a Fortran project using CMake as the build system

CMake Fortran Template

I have found there is a dirth of information about how to create Fortran projects with CMake on the web. For this reason, I have created a template project for Fortran using CMake as the build system.

The directory structure

CMakeLists.txt
README.md
bin/
cmake/
    Modules/
        FindOpenMP_Fortran.cmake
        SetCompileFlag.cmake
        SetFortranFlags.cmake
        SetParallelizationLibrary.cmake
        SetUpLAPACK.cmake
distclean.cmake
lib/
src/
    foo/
        CMakeLists.txt
        foo.f90
        constants.f90
    bar/
        CMakeLists.txt
        bar.f90

CMakeLists.txt

This file contains all the boilerplate that you will need to set up your program. Pretty much all you will need to edit in this file is the name of the project/program and uncomment any lines pertaining to options you may need.

distclean.cmake

This is a CMake script that will remove all files and folder that are created after running make. You can run this code in one of two ways:

• Execute cmake -P distclean.cmake. (The -P option to cmake will execute a CMake script)
• Execute make distclean after your Makefile has been generated.

You shouldn't need to edit this file.

cmake/Modules/

This directory contains CMake scripts that aid in configuring the build system.

FindOpenMP_Fortran.cmake

The FindOpenMP.cmake file that comes with CMake does not have support for Fortran compilers. This file finds the correct OpenMP flags for many Fortran compilers.

SetCompileFlag.cmake

This file defines a function that will test a set of compiler flags to see which one works and adds that flag to a list of compiler flags. This is used to set compile flags when you don't know which compiler will be used.

SetFortranFlags.cmake

This file uses the function from SetCompilerFlag.cmake to set the DEBUG, TESTING, and RELEASE compile flags for your build. You might want to inspect this file and edit the flags to your liking.

SetParallelizationLibrary.cmake

This file takes care of locating OpenMP or MPI as well as issues with switching between the two.

SetUpLAPACK.cmake

This file takes care of some oddities with CMake related to setting up LAPACK, such as the fact that the LAPACK variables are not saved to the cache, and that finding MKL requires a C compiler.

src/

This directory contains the source for your project. In this project example, there is a library (in bar/) and the executable itself (in foo/). Each of these subdirectories contains a CMakeLists.txt.

bar/CMakeLists.txt

All that is contained in this file is a list of the source files for the library bar and a statement that these sources should be compiled to a library. You will need to edit the source list (and the STATIC modifier to SHARED if you want a shared library instead of static.).

foo/CMakeLists.txt

This file contains the sources for the foo executable. It also specifies that this executable must link to the bar library. You will need to edit the source list (and whether or not there are libraries to link to). There is commented code related to parallelization and LAPACK that you may uncomment if required.

bin/ and lib/

These folders are created after running make. Any libraries created end up in lib/, as well as compiled Fortran .mod files. The executable will end up in bin/.

Configuring the build

It is usually preferred that you do an out-of-source build. To do this, create a build/ directory at the top level of your project and build there.

$ mkdir build
$ cd build
$ cmake ..
$ make

When you do this, temporary CMake files will not be created in your src/ directory.

As written, this template will allow you to specify one of three different sets of compiler flags. The default is RELEASE. You can change this using to TESTING or DEBUG using

$ cmake .. -DCMAKE_BUILD_TYPE=DEBUG

or

$ cmake .. -DCMAKE_BUILD_TYPE=TESTING

There are also options you may uncomment to add support for OpenMP or MPI. To use these, use

$ cmake .. -DUSE_OPENMP=ON

or

$ cmake .. -DUSE_MPI=ON

Of course, you can also edit the template so that OpenMP or MPI is always used.