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Coding Style

General

  • Trim all trailing whitespace from every line (some editors can do this automatically).
  • No characters.
  • Supply a header for each file with a description of the file and the author(s) name or GitHub ID.
  • A copy of the Gnu Lesser General Public License must be included at the top of each file.
  • Documentation should be written so that it can be parsed by Doxygen.
  • All variables should be defined, and include units. Unit-less variables should be marked unitless
  • Provide detailed descriptions of modules, interfaces, functions, and subroutines
  • Define all function/subroutine arguments, and function results (see below)
  • Follow coding style of the current file, as much as possible.

Fortran

General

  • Use Fortran 95 standard or newer
  • Two space indentation
  • Use KIND parameters from platform_mod
  • Never use implicit variables (i.e., always specify IMPLICIT NONE)
  • Lines must be <= 120 characters long (including comments)
  • logical, compound logical, and relational if statements may be one line, using “&” for line continuation if necessary: 
    if(file_exists(fileName)) call open_file(fileObj,fileName, is_restart=.false)
  • Avoid the use of GOTO statements
  • Avoid the use of Fortran reserved words as variables (e.g. DATA, NAME)
  • Avoid the use of COMMON blocks

Derived types

  • Type names must be in CapitalWord format.
  • Variables names must be in underscore_word format.
  • All member variables must be private.
  • Doxygen description on the line before the type definition.
  • Inline doxygen descriptions for all member variables.

Functions

  • If a function has a result variable, it should be declared on its own line, and the variable should not be declared with a specific intent.
  • Inline doxygen descriptions for all arguments, except the result variable.
  • Doxygen description on the line(s) before the function definition. This must specify what the function is returning using the @return doxygen keyword.

Blocks

  • terminate do loops with enddo
  • terminate block if, then statements with endif

OpenMP

  • Directives should start at the beginning of the line, and be in lowercase.
  • All openMP directives should specify default(none), and then explicitly list all shared and private variables.
  • All critical sections must have a unique name.

Precision

  • Precision of all real arguments are explicitly defined as real(kind=r4_kind), real(kind=r8_kind), or as any other precision parameters defined in platform_mod.
  • The precision of real numerical values should be consistent with the precision of the associated variable. For example, if the variable a has been declared as r8_kind, then a=1.4_r8_kind is acceptable. The following, a=1.4 and a=(1.4,kind=r8_kind), are not acceptable since the numerical value of 1.4 will be represented in the default precision set by the compiler.
  • The precision of integers do not need to be explicitly defined and can be determined at compile time.
  • If the precision of integers are explicitly defined, they are defined with the precision parameters, e.g. i4_kind, i8_kind, found in platform_mod.

Macros

  • All letters in the macro names are capitalized
  • All macro names end with an underscore "_"
  • All precision related macro names start with the letters "FMS"
  • Macro names should be unique to each module. For example, FMS_AU_KIND_ is used in axis_utils_mod. FMS_HI_KIND_ is used in horiz_interp_mod

.fh and .inc files

  • The .fh header files contain macro definitions.
  • If the .fh files contain mainly precision related macro definitions, the files should be named with _r4.fh and _r8.fh extensions in the include subdirectory found in the module directory. These .fh files are #include-ed at the end of the .F90 module files.
  • For precision related .inc files, the .inc files contain the procedure definitions and are #include-ed at the end of both *_r4.fh and *_f8.fh files. These .inc files are located in the same include subdirectory as the .fh files. See below for details.

Fortran Example

!***********************************************************************
!*                   GNU Lesser General Public License
!*
!* This file is part of the GFDL Flexible Modeling System (FMS).
!*
!* FMS is free software: you can redistribute it and/or modify it under
!* the terms of the GNU Lesser General Public License as published by
!* the Free Software Foundation, either version 3 of the License, or (at
!* your option) any later version.
!*
!* FMS is distributed in the hope that it will be useful, but WITHOUT
!* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
!* FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
!* for more details.
!*
!* You should have received a copy of the GNU Lesser General Public
!* License along with FMS.  If not, see <http://www.gnu.org/licenses/>.
!***********************************************************************

!> @file
!! @brief Example code
!! @author <developer>
!! @email gfdl.climate.model.info@noaa.gov

module example_mod
  use platform_mod, only r4_kind, r8_kind, i4_kind, i8_kind
  use util_mod, only: util_func1
  implicit none
  private

  public :: sub1
  public :: func1
  public :: ex_subroutine

  interface ex_subroutine             !< generic interface block.  When the user
    module procedure ex_subroutine_r4 !! calls ex_subroutine, the compiler checks
    module procedure ex_subroutine_r8 !! the input arguments and invokes either
  end interface ex_subroutine         !! ex_subroutine_r4 or ex_subroutine_r8
                                      !! ex_subroutine_r4/8 are generated by the preprocessor
                                      !! which requires example_r4.fh, example_r8.fh, and
                                      !! example.inc files

  !> @brief Doxygen description of type.
  type,public :: CustomType
    private
    integer(kind=i4_kind) :: a_var !< Inline doxygen description.
    real(kind=r8_kind),dimension(:),allocatable :: b_arr !< long description
                                                         !! continued on
                                                         !! multiple lines.
  endtype CustomType

  contains

  !> @brief Doxygen description.
  subroutine sub1(arg1, arg2, &
    & arg3)
    real(kind=r4_kind),intent(in) :: arg1 !< Inline doxygen description.
    integer(kind=i8_kind),intent(inout) :: arg2 !< Inline doxygen description.
    character(len=*),intent(inout) :: arg3 !< Long inline doxygen
                                           !! description.

    arg1=2.456_r4_kind
  end subroutine sub1

  !> @brief Doxygen description
  !! @return Function return value.
  function func1(arg1, arg2) result(res)
    integer(kind=i4_kind),intent(in) :: arg1 !< Inline doxygen description
    integer(kind=i4_kind),intent(in) :: arg2 !< Inline doxygen description
    integer(kind=r8_kind) :: res

    res=real(arg1,r8_kind) * 3.14_r8_kind
  end function func1

#include "example_r4.fh" !< These two header file contains the macro definition
#include "example_r8.fh" !! and an "#include example.inc" where the procedure
                         !! is defined.  See below.
end module example_mod
!***********************************************************************
!*                   GNU Lesser General Public License
!*
!* This file is part of the GFDL Flexible Modeling System (FMS).
!*
!* FMS is free software: you can redistribute it and/or modify it under
!* the terms of the GNU Lesser General Public License as published by
!* the Free Software Foundation, either version 3 of the License, or (at
!* your option) any later version.
!*
!* FMS is distributed in the hope that it will be useful, but WITHOUT
!* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
!* FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
!* for more details.
!*
!* You should have received a copy of the GNU Lesser General Public
!* License along with FMS.  If not, see <http://www.gnu.org/licenses/>.
!***********************************************************************

!> @file
!! @brief Example _r4.fh file containing macro definitions
!! @author <developer>
!! @email gfdl.climate.model.info@noaa.gov

#undef   FMS_EX_KIND_
#define  FMS_EX_KIND_ r4_kind

#undef  EX_SUBROUTINE_
#define EX_SUBROUTINE_ ex_subroutine_r4

#include "example.inc" !< example.inc file contains the procedure definition
!***********************************************************************
!*                   GNU Lesser General Public License
!*
!* This file is part of the GFDL Flexible Modeling System (FMS).
!*
!* FMS is free software: you can redistribute it and/or modify it under
!* the terms of the GNU Lesser General Public License as published by
!* the Free Software Foundation, either version 3 of the License, or (at
!* your option) any later version.
!*
!* FMS is distributed in the hope that it will be useful, but WITHOUT
!* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
!* FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
!* for more details.
!*
!* You should have received a copy of the GNU Lesser General Public
!* License along with FMS.  If not, see <http://www.gnu.org/licenses/>.
!***********************************************************************

!> @file
!! @brief Example file _r8.fh file containing macro definitions
!! @author <developer>
!! @email gfdl.climate.model.info@noaa.gov

#undef   FMS_EX_KIND_
#define  FMS_EX_KIND_ r8_kind

#undef  EX_SUBROUTINE_
#define EX_SUBROUTINE_ ex_subroutine_r8

#include "example.inc" !< example.inc file contains the procedure definition
!***********************************************************************
!*                   GNU Lesser General Public License
!*
!* This file is part of the GFDL Flexible Modeling System (FMS).
!*
!* FMS is free software: you can redistribute it and/or modify it under
!* the terms of the GNU Lesser General Public License as published by
!* the Free Software Foundation, either version 3 of the License, or (at
!* your option) any later version.
!*
!* FMS is distributed in the hope that it will be useful, but WITHOUT
!* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
!* FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
!* for more details.
!*
!* You should have received a copy of the GNU Lesser General Public
!* License along with FMS.  If not, see <http://www.gnu.org/licenses/>.
!***********************************************************************
!> @file
!! @brief Example .inc file containing subroutine definitions/declarations
!! @author <developer>
!! @email gfdl.climate.model.info@noaa.gov

!> The macro EX_SUBROUTINE_ gets replaced by the preprocessor
!! as ex_subroutine_r4 (as defined in the example_r4.fh file) and
!! as ex_subroutine r8 (as defined in the example_r8.fh file)

subroutine EX_SUBROUTINE_(arg1, arg2, arg3)
  real(FMS_EX_KIND_), intent(in)  :: arg2 !< FMS_EX_KIND_ gets replaced by the preprocessor
  real(FMS_EX_KIND_), intent(out) :: arg1 !< FMS_EX_KIND_ gets replaced by the preprocessor
  integer(i4_kind) :: arg3
  integer, parameter :: lkind=FMS_EX_KIND_ !< kind parameter local to the subroutine

  arg1 = arg2 / 4.0_lkind !< GCC does not like 4.0_FMS_EX_KIND_.  Thus, the
                          !! parameter lkind is declared and used.

end subroutine EX_SUBROUTINE_

C/C++

General

  • C code is written in GNU style. Each new level in a program block is indented by 2 spaces. Braces start on a new line, and are also indented by 2 spaces.
  • See the Gnome C coding style guide for more information