Policies/Frameworks Coding Style

Note

This document describes the recommended coding style for KDE Frameworks. Nobody is forced to use this style, but to have consistent formatting of the source code files it is recommended to make use of it.

In short: KDE Frameworks coding style follows the Qt coding style, with one main difference: using curly braces even when the body of a conditional statement contains only one line.

Indentation

No tabs
4 Spaces instead of one tab

Variable declaration

Each variable should be declared on a new line
Each new word in a variable name starts with a capital letter (so-called camelCase)
Avoid abbreviations
Use indicative/useful names. No short names, except:
- Single character variable names can denote counters and temporary variables whose purpose is obvious
Variables and functions start with a lowercase letter
Member variable names should be prefixed with m_ to make it easier to distinguish them from function parameters and local variable names
- The same applies to Private (d-pointer) class member variable names, (it may be a bit overkill when the Private class is merely used as a struct and all the code is in the public class, so you can use the m_ prefix everywhere to keep it consistent, or switch to prefixing m_ when adding the first method to a Private class)
Static (global) variable names should be prefixed with s_

Example: </translate>

<translate>
// Local variable declarations, wrong</translate>
KProgressBar *prbar;
QString prtxt, errstr;

<translate>
// Local variable declarations, correct</translate>
KProgressBar *downloadProgressBar;
QString progressText;
QString errorString;

<translate>
// Member variable declarations, wrong </translate>
bool isActiveView = false;
QVBoxLayout *boxLayout = nullptr;

<translate>
// Member variable declarations, correct </translate>
bool m_isValid = false;
QVBoxLayout *m_boxLayout = nullptr;;

Whitespace

Use blank lines to group statements
Use only one empty line
Use one space after each keyword
For pointers or references, use a single space before '*' or '&', but not after
No space after a cast

Example: </translate>

<translate><!--T:10-->
// wrong</translate>
QString* myString;
if(true){
}

<translate><!--T:11-->
// correct</translate>
QString *myString;
if (true) {
}

Braces

As a base rule, the left curly brace goes on the same line as the start of the statement.

Example: </translate>

<translate><!--T:14-->
// wrong</translate>
if (true)
{
}

<translate><!--T:15-->
// correct</translate>
if (true) {
}

<translate> Exception: Function implementations, class, struct and namespace declarations always have the opening brace on the start of a line.

Example: </translate>

void debug(int i)
{
    qDebug("foo: %i", i);
}

class Debug
{
};

<translate> Use curly braces even when the body of a conditional statement contains only one line.

Example: </translate>

<translate><!--T:20-->
// wrong</translate>
if (true)
    return true;

for (int i = 0; i < 10; ++i)
    qDebug("%i", i);

<translate><!--T:21-->
// correct</translate>
if (true) {
    return true;
}

for (int i = 0; i < 10; ++i) {
    qDebug("%i", i);
}

Switch statements

Case labels are on the same column as the switch

Example: </translate>

switch (myEnum) {
case Value1:
    doSomething();
    break;
case Value2:
    doSomethingElse();
    // fall through
default:
    defaultHandling();
    break;
}

Line breaks

Try to keep lines shorter than 100 characters, inserting line breaks as necessary.

Qt Includes

If you add #includes for Qt classes, use only the class name.

Example: </translate>

<translate><!--T:27-->
// wrong</translate>
#include <QtCore/QString>

<translate><!--T:28-->
// correct</translate>
#include <QString>

Artistic Style (astyle) automatic code formatting

You can use astyle (>=1.23) to format code or to test if you have followed this document. Run the following command: </translate>

astyle --indent=spaces=4 --brackets=linux \
       --indent-labels --pad=oper --unpad=paren \
       --one-line=keep-statements --convert-tabs \
       --indent-preprocessor \
       `find -type f -name '*.cpp'-or -name '*.cc' -or -name '*.h'`

<translate> With astyle (>=2.01) you need to run the following command: </translate>

astyle --indent=spaces=4 --style=linux \
       --indent-labels --pad-oper --unpad-paren --pad-header \
       --keep-one-line-statements --convert-tabs \
       --indent-preprocessor \
       `find -type f -name '*.cpp' -or -name '*.cc' -or -name '*.h'`

<translate> Note: With more recent astyle --brackets has become --style, so change --brackets=linux to --style=linux.

You can find a shell script to run this command in:

kde-dev-scripts/astyle-kdelibs (POSIX)
kde-dev-scripts/astyle-kdelibs.bat (Windows)

Emacs and Vim scripts

The kde-dev-scripts directory in the kdesdk module contains, among other useful things, some useful additions to the Emacs and Vim text editors that make it easier to edit KDE code with them.

Emacs

The kde-emacs directory contains a set of key bindings, macros and general useful code. It is compatible with both GNU Emacs and XEmacs.

To start using kde-emacs, add the following to your .emacs: </translate>

(add-to-list 'load-path "/path/to/kde-emacs")
(require 'kde-emacs)

<translate> Many settings can be changed by editing the "kde-emacs" group via M-x customize-group.

For more information, including what the key bindings are and what additional settings you could add to your .emacs, please check kde-emacs.el itself.

Vim

You can find a vim script in kde-devel-vim.vim that helps you to keep the coding style correct. In addition to defaulting to the KDE Frameworks coding style it will automatically use the correct style for Solid and kdepim code. If you want to add rules for other projects feel free to add them in the SetCodingStyle function.

To use the script, include it in your ~/.vimrc like this: </translate>

source /path/to/kde/sources/kdesdk/scripts/kde-devel-vim.vim

<translate> Document started by Urs Wolfer. Some parts of this document have been adopted from the Qt Coding Style document posted by Zack Rusin on kde-core-devel. </translate>