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dev:codingconventions [2018/12/19 11:37] – raise Fortran standard to 2008 since we are already using features from there tmuellerdev:codingconventions [2026/10/14 08:40] (current) – fstein
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 ====== Coding Conventions ====== ====== Coding Conventions ======
  
-===== Stick to the standard ===== +This page has been moved to [[https://manual.cp2k.org/trunk/development/coding-conventions.html]]
- +
-  * Code enabled by default should be standard Fortran2008 [-std=f2008] +
-  * OpenMP code should follow the version 3.X of the standard +
-  * MPI should should follow the version 3 of the standard +
-  * Extended functionality should match [[wp>POSIX]] / [[wp>Linux_Standard_Base|LSB]]. +
- +
-===== Write explicit code ===== +
-  * Every ''USE''-statement should have an ''ONLY:''-clause, which lists the imported symbols [-Wuse-without-only]. +
-  * Every ''OMP PARALLEL''-region should declare ''default(none)''. +
-  * Every static variable should be marked with the ''SAVE'' attribute. +
-  * Every Fortran module should contain the line ''IMPLICIT NONE'' [-fimplicit-none]. +
-  * Every conversion that might change value should be explicit [-Wconversion]. Rationale: +
-    * INTEGER i=4.9999, i.e. i=INT(4.9999) implies i==4. Use NINT(4.9999) as appropriate. +
-    * natom*natom, nrow_global*ncol_global overflows INT(KIND=4) for large simulations. +
-    * always use REAL() with KIND parameter, i.e. r = REAL(i, KIND=dp). +
-    * avoid FLOAT() in favour of REAL(, KIND=dp). +
-    * the global number of grid points (pw_grid_type%ngpts,ngpts_cut) overflows INT(KIND=4) for large simulations. +
- +
-===== Don't use poorly designed language features ===== +
-  * Do not use the ''GOTO''-statement. See also [[http://xkcd.com/292/]] and [[doi>10.1145/362929.362947]] +
-  * Do not use left-hand-side (lhs) reallocations of allocatables [-Wrealloc-lhs-all]. [[http://www.tddft.org/pipermail/octopus-devel/2012-February/005510.html | Why? ]]  +
-  * Do not use ''FORALL'' constructs. [[https://gcc.gnu.org/ml/fortran/2012-04/msg00025.html | Why? ]] +
-  * Do not use ''OMP THREADPRIVATE'' variables. +
-  * Do not query the ''STAT'' from a ''DEALLOCATE'', the Fortran runtime takes care. +
-  * Do not use ''RANDOM_NUMBER()'', it's not consistent across different compilers. +
- +
-===== Fight spaghetti code ===== +
-There are two measure of defense against [[wp>Spaghetti_code|spaghetti code]]: +
-  - Decoupling on the module and package level: +
-     * Every module should depend on as few other modules as possible. +
-     * Every package should depend on as few other packages as possible. +
-  - [[wp>Information_hiding|Information hiding]], also known as encapsulation.  +
-     * External libraries should be wrapped within a single module or package. +
-     * Every module should hide its content by containing the line ''PRIVATE'' and only few public symbols. +
-     * Every package should hide its content by providing only a small public API through a single module. +
- +
-===== Use existing infrastructure ===== +
-For many common operations there exist wrappers in CP2K to prevent usage errors and to allow for central redirections, i.e. avoid to use direct calls to external libraries in CP2K +
-  * Use the routines from ''cp_files.F'' instead of calling ''OPEN'' and ''CLOSE'' directly. +
-  * Use the routines from the full-matrix ''fm''-package instead of calling BLAS or Scalapack directly. +
-  * Use the routines from ''message_passing.F'' instead of calling MPI directly. +
-  * Use the routines from ''fft_lib.F'' instead of calling FFT (any library) directly. +
-  * Use the routines from ''machine.F'' to access architecture depended things like e.g. the working directory. +
-  * Don't use ''UNIT=*'' in ''WRITE'' or ''PRINT'' statements. Instead request a unit from the logger: ''iw=cp_logger_get_default_unit_nr()'' and write only if you actually received a unit: ''IF(iw>0) WRITE (UNIT=iw, ,,,)''. +
-  * Use [[error_handling|CP2K's error-handling]], instead of the ''STOP'' statement. +
- +
-===== Remove dead code ===== +
-  * Every line of code has to be compiled and maintained. Hence, unused variables and code poses an unnecessary burden and should be removed [-Wunused-variable -Wunused-but-set-variable -Wunused-dummy-argument]. +
-  * Sometimes it is beneficial to keep debugging code around nevertheless. Such code should be put into a ''IF(debug_this_module)''-block, with a parameter set to ''.FALSE.''. This way the code will stay up-to-date and easily callable. +
- +
-===== Format and document code ===== +
-  * Each files should start with the official CP2K header. +
-  * Each ''.F'' file should contain either a ''PROGRAM'' or a single ''MODULE'', whose name matches the filename. +
-  * Each module and routine should be annotated with [[dev:codingconventions#Doxygen| Doxygen documentation]]. +
-  * Each preprocessor flag should start with two underscores and be documented in the ''INSTALL''-file and added to the cp2k_flags function (cp2k_info.F). +
-  * The code should be formatted with the [[dev:formattingconventions| prettify tool]] by running ''make -j pretty''. +
-===== Write tests ===== +
-  * Every feature should be tested, with the goal of complete [[ http://www.cp2k.org/static/coverage/ | code coverage by regtesting ]]. +
- +
-===== Doxygen documentation ===== +
- +
-  * Every ''FUNCTION'' and ''SUBROUTINE'' should be preceded by a valid doxygen block. +
-  * The following keywords are required: ''\brief'', ''\param'' (for each parameter), ''\retval'' (for functions) +
-  * The following keywords are optional: ''\note'', ''\par'', ''\date'', ''\author'' +
-  * Please run ''make doxify'' to format your doxygen comments, or generate templates where none exist +
-  * See our [[ http://doxygen.cp2k.org/files.html | doxygen pages ]] for the result+
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