CODING

intensively (except for file headers).

This document provides an introduction in how the source code of libelektra is organized and how and where to add functionality.

Make sure to read DESIGN together with this document.

Folder structure

After you downloaded and unpacked Elektra you see unusually many folders. The reason is that the Elektra project consists of many activities.

The most important are:

• src: This directory contains the source of the library and the tools.
• doc: Documentation for the library
• example: Examples on how to use the library
• tests: contains the testing framework for the source.

Source Code

libelektra is the ANSI/ISO C-Core which coordinates the interactions between the user and the plugins.

The plugins have all kinds of dependencies. It is the responsibility of the plugins to find and check them using CMake. The same guidelines apply to all code in the repository including the plugins.

libloader is responsible for loading the backend modules. It works on various operating systems by using libltdl. This code is optimized for static linking and win32.

kdb is the commandline-tool to access and initialize the Elektra database.

General Guidelines

You are only allowed to break a guideline if there is a good reason to do so. When you do, document the fact, either in the commit message, or as comment next to the code.

Of course, all rules of good software engineering apply: Use meaningful names and keep the software both testable and reusable.

The purpose of the guidelines is to have a consistent style, not to teach programming.

If you see broken guidelines do not hesitate to fix them. At least put a TODO marker to make the places visible.

If you see inconsistency do not hesitate to talk about it with the intent to add a new rule here.

See DESIGN document too, they complement each other.

Coding Style

• Limits
  • Functions should not exceed 100 lines.
  • Files should not exceed 1000 lines.
  • A line should not be longer than 140 characters.

Split up when those limits are reached. Rationale: Readability with split windows.

• Indentation
  • Use tabs for indentation.
  • One tab equals 8 spaces.
• Blocks
  • Use blocks even for single line statements.
  • Curly braces go on a line on their own on the previous indentation level.
  • Avoid multiple variable declarations at one place.
  • Declare Variables as late as possible, preferable within blocks.
• Naming
  • Use camelCase for functions and variables.
  • Start types with upper-case, everything else with lower-case.
  • Prefix names with elektra for internal usage. External API either starts with ks, key or kdb.
• Comments
  • Use C-comments /**/ with doxygen style for functions.
  • Use C++-comments // for single line statements about the code in the next line.
• Whitespaces
  • Use space before and after equal when assigning a value.
  • Use space before round parenthesis ( ( ).
  • Use space before and after * from Pointers.
  • Use space after , of every function argument.

C Guidelines

• The compiler shall not emit any warning (or error).
• Use goto only for error situations.
• Use const as much as possible.
• Use static methods if they should not be externally visible.
• C-Files have extension .c, Header files .h.

Example: src/libs/elektra/kdb.c

C++ Guidelines

• Everything as in C if not noted otherwise.
• Do not use goto at all, use RAII instead.
• Do not use raw pointers, use smart pointers instead.
• C++-Files have extension .cpp, Header files .hpp.
• Do not use static, but anonymous namespaces.
• Write everything within namespaces and do not prefix names.
• Even though we use C++11, we should be oriented towards https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md "more safe and modern usage"

Example: src/bindings/cpp/include/kdb.hpp

Doxygen Guidelines

doxygen is used to document the API and to build the html and pdf output. We also support the import of Markdown pages. Doxygen 1.8.8 or later is required for this feature (Anyways you can find the API Doc online). Links between Markdown files will be converted with the Markdown Link Converter. Markdown pages are used in the pdf, therefore watch which characters you use and provide a proper encoding!

• use @ to start Doxygen tags
• Do not duplicate information available in git in Doxygen comments.
• Use \copydetails, @copybrief and @copydetails intensively (except for file headers).

File Headers

Files should start with:

        /**
         * @file
         *
         * @brief <short statement about the content of the file>
         *
         * @copyright BSD License (see doc/COPYING or http://www.libelektra.org)
         */

Note:

• @ file has no parameters.
• @ brief should contain a short statement about the content of the file and is needed so that your file gets listed at http://doc.libelektra.org/api/latest/html/files.html

The duplication of the filename, author and date is not needed, because this information is tracked using git and doc/AUTHORS already.