Difference between revisions of "Policies/Frameworks Coding Style"

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This document describes the recommended coding style for kdelibs. Nobody is forced to use this style, but to have consistent formating of the source code files it is recommended to take use of it.
+
<languages />
 +
<translate>
  
'''In short: Kdelibs coding style follows the Qt 4 coding style.'''
+
{{Note|1=<!--T:1-->
 +
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.
  
== Indentation ==
+
 
 +
<!--T:2-->
 +
'''In short: KDE Frameworks coding style follows the [http://wiki.qt.io/Qt_Coding_Style Qt coding style], with one main difference: using curly braces even when the body of a conditional statement contains only one line.'''}}
 +
 
 +
== Indentation == <!--T:3-->
 
* No tabs
 
* No tabs
 
* 4 Spaces instead of one tab
 
* 4 Spaces instead of one tab
  
== Variable delclaration ==
+
== Variable declaration == <!--T:4-->
 
* Each variable declaration on a new line
 
* Each variable declaration on a new line
* Take useful names, no short names, except:
+
* Each new word in a variable name starts with a capital letter (so-called camelCase)
* Single character variable names can be used for counters and temporary variables, where the purpose is obvious
 
* Variables and functions start with a small letter
 
* Each new word in a variable name starts with a capital letter
 
 
* Avoid abbreviations
 
* Avoid abbreviations
 +
* Take 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
  
 +
<!--T:5-->
 
Example:
 
Example:
<code cppqt>
+
</translate>
// wrong
+
<syntaxhighlight lang="cpp-qt">
 +
<translate><!--T:6-->
 +
// wrong</translate>
 
KProgressBar *prbar;
 
KProgressBar *prbar;
 
QString prtxt, errstr;
 
QString prtxt, errstr;
  
// correct
+
<translate><!--T:7-->
 +
// correct</translate>
 
KProgressBar *downloadProgressBar;
 
KProgressBar *downloadProgressBar;
 
QString progressText;
 
QString progressText;
 
QString errorString;
 
QString errorString;
</code>
+
</syntaxhighlight>
  
== Whitespace ==
+
<translate>
 +
 
 +
== Whitespace == <!--T:8-->
 
* Use blank lines to group statements
 
* Use blank lines to group statements
 
* Use only one empty line
 
* Use only one empty line
Line 34: Line 46:
 
* No space after a cast
 
* No space after a cast
  
 +
<!--T:9-->
 
Example:
 
Example:
<code cppqt>
+
</translate>
// wrong
+
<syntaxhighlight lang="cpp-qt">
 +
<translate><!--T:10-->
 +
// wrong</translate>
 
QString* myString;
 
QString* myString;
 
if(true){
 
if(true){
 
}
 
}
  
// correct
+
<translate><!--T:11-->
 +
// correct</translate>
 
QString *myString;
 
QString *myString;
 
if (true) {
 
if (true) {
 
}
 
}
</code>
+
</syntaxhighlight>
  
== Braces ==
+
<translate>
 +
== Braces == <!--T:12-->
 
As a base rule, the left curly brace goes on the same line as the start of the statement.
 
As a base rule, the left curly brace goes on the same line as the start of the statement.
  
 +
<!--T:13-->
 
Example:
 
Example:
<code cppqt>
+
</translate>
// wrong
+
<syntaxhighlight lang="cpp-qt">
 +
<translate><!--T:14-->
 +
// wrong</translate>
 
if (true)
 
if (true)
 
{
 
{
 
}
 
}
  
// correct
+
<translate><!--T:15-->
 +
// correct</translate>
 
if (true) {
 
if (true) {
 
}
 
}
</code>
+
</syntaxhighlight>
  
Exception: Function implementations and class declarations always have the left brace on the start of a line.
+
<translate>
 +
<!--T:16-->
 +
Exception: Function implementations, class, struct and namespace declarations always have the opening brace on the start of a line.
  
 +
<!--T:17-->
 
Example:
 
Example:
<code cppqt>
+
</translate>
 +
<syntaxhighlight lang="cpp-qt">
 
void debug(int i)
 
void debug(int i)
 
{
 
{
Line 74: Line 99:
 
{
 
{
 
};
 
};
</code>
+
</syntaxhighlight>
  
Use curly braces when the body of a conditional statement contains more than one line, and also if a single line statement is somewhat complex.
+
<translate>
 +
<!--T:18-->
 +
Use curly braces even when the body of a conditional statement contains only one line.
  
 +
<!--T:19-->
 
Example:
 
Example:
<code cppqt>
+
</translate>
// wrong
+
<syntaxhighlight lang="cpp-qt">
if (true) {
+
<translate><!--T:20-->
    return true;
+
// wrong</translate>
}
 
 
 
for (int i = 0; i < 10; ++i) {
 
    qDebug("%i", i);
 
}
 
 
 
// correct
 
 
if (true)
 
if (true)
 
     return true;
 
     return true;
Line 95: Line 116:
 
for (int i = 0; i < 10; ++i)
 
for (int i = 0; i < 10; ++i)
 
     qDebug("%i", i);
 
     qDebug("%i", i);
</code>
 
  
Exception 1: Use braces also if the parent statement covers several lines or wraps.
+
<translate><!--T:21-->
 
+
// correct</translate>
Example:
+
if (true) {
<code cppqt>
 
if (address.isEmpty() || !isValid()
 
    || !codec) {
 
    return false;
 
}
 
</code>
 
 
 
Exception 2: Use braces also in if-then-else blocks where either the if-code or the else-code covers several lines.
 
 
 
Example:
 
<code cppqt>
 
// wrong
 
if (true)
 
 
     return true;
 
     return true;
else {
 
    ++it;
 
    return false;
 
 
}
 
}
  
// correct
+
for (int i = 0; i < 10; ++i) {
if (true) {
+
     qDebug("%i", i);
    return true;
 
} else {
 
    ++it;
 
     return false;
 
 
}
 
}
</code>
+
</syntaxhighlight>
  
== Switch statements ==
+
<translate>
 +
== Switch statements == <!--T:22-->
 
Case labels are on the same column as the switch
 
Case labels are on the same column as the switch
  
 +
<!--T:23-->
 
Example:
 
Example:
<code cppqt>
+
</translate>
 +
<syntaxhighlight lang="cpp-qt">
 
switch (myEnum) {
 
switch (myEnum) {
 
case Value1:
 
case Value1:
Line 144: Line 147:
 
     break;
 
     break;
 
}
 
}
</code>
+
</syntaxhighlight>
 +
 
 +
<translate>
 +
== Line breaks == <!--T:24-->
 +
Try to keep lines shorter than 100 characters, inserting line breaks as necessary.
 +
 
 +
== Qt Includes == <!--T:25-->
 +
* If you add #includes for Qt classes, use only the  class name.
 +
 
 +
<!--T:26-->
 +
Example:
 +
</translate>
 +
<syntaxhighlight lang="cpp-qt">
 +
<translate><!--T:27-->
 +
// wrong</translate>
 +
#include <QtCore/QString>
 +
 
 +
<translate><!--T:28-->
 +
// correct</translate>
 +
#include <QString>
 +
</syntaxhighlight>
 +
 
 +
<translate>
 +
 
 +
== Artistic Style (astyle) automatic code formatting == <!--T:29-->
 +
You can use [http://astyle.sourceforge.net/ astyle] (>=1.23) to format code or to test if you have followed this document. Run the following command:
 +
</translate>
 +
<syntaxhighlight lang="text">
 +
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'`
 +
</syntaxhighlight>
 +
 
 +
<translate>
 +
<!--T:30-->
 +
With astyle (>=2.01) you need to run the following command:
 +
</translate>
 +
<syntaxhighlight lang="text">
 +
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'`
 +
</syntaxhighlight>
 +
 
 +
<translate>
 +
<!--T:31-->
 +
Note: With more recent astyle --brackets has become --style, so change --brackets=linux to --style=linux.
 +
 
 +
<!--T:41-->
 +
You can find a shell script to run this command in:
 +
 
 +
<!--T:40-->
 +
* [https://commits.kde.org/kde-dev-scripts?path=astyle-kdelibs kde-dev-scripts/astyle-kdelibs] (POSIX)
 +
* [https://commits.kde.org/kde-dev-scripts?path=astyle-kdelibs.bat kde-dev-scripts/astyle-kdelibs.bat] (Windows)
 +
 
 +
== Emacs and Vim scripts == <!--T:32-->
 +
The [https://projects.kde.org/projects/kde/kdesdk/kde-dev-scripts/repository/revisions/master/show 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 [https://projects.kde.org/projects/kde/kdesdk/kde-dev-scripts/repository/revisions/master/show/kde-emacs kde-emacs] directory contains a set of key bindings, macros and general useful code. It is compatible with both GNU Emacs and XEmacs.
 +
 
 +
<!--T:33-->
 +
To start using kde-emacs, add the following to your .emacs:
 +
</translate>
 +
 
 +
<syntaxhighlight lang="text">
 +
(add-to-list 'load-path "/path/to/kde-emacs")
 +
(require 'kde-emacs)
 +
</syntaxhighlight>
 +
 
 +
<translate>
 +
<!--T:34-->
 +
Many settings can be changed by editing the "kde-emacs" group via <tt>M-x customize-group</tt>.
 +
 
 +
<!--T:35-->
 +
For more information, including what the key bindings are and what additional settings you could add to your .emacs, please check <tt>kde-emacs.el</tt> itself.
 +
 
 +
=== Vim === <!--T:36-->
 +
You can find a vim script in [https://projects.kde.org/projects/kde/kdesdk/kde-dev-scripts/repository/revisions/master/raw/kde-devel-vim.vim 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.
  
== Artistic Style (astyle) automatic code formatting ==
+
<!--T:37-->
You can use [http://astyle.sourceforge.net/ astyle] (<=1.19) to format code or to test if you have followed this document. Run the following command:
+
To use the script, include it in your {{path|~/.vimrc}} like this:
<code>
+
</translate>
astyle --indent=spaces=4 --brackets=linux --indent-labels --pad=oper --unpad=paren --one-line=keep-statements --convert-tabs --indent-preprocessor
+
<syntaxhighlight lang="text">
`find -type f -name '*.cpp'` `find -type f -name '*.h'`
+
source /path/to/kde/sources/kdesdk/scripts/kde-devel-vim.vim
</code>
+
</syntaxhighlight>
  
  
 +
<translate>
 +
<!--T:38-->
 
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.
 
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.
  
 +
<!--T:39-->
 
[[Category:Policies]] [[Category:C++]]
 
[[Category:Policies]] [[Category:C++]]
 +
</translate>

Latest revision as of 09:57, 31 October 2019


Note-box-icon.png
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 declaration on a new line
  • Each new word in a variable name starts with a capital letter (so-called camelCase)
  • Avoid abbreviations
  • Take 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

Example:

// wrong
KProgressBar *prbar;
QString prtxt, errstr;

// correct
KProgressBar *downloadProgressBar;
QString progressText;
QString errorString;


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:

// wrong
QString* myString;
if(true){
}

// correct
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:

// wrong
if (true)
{
}

// correct
if (true) {
}

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

Example:

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

class Debug
{
};

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

Example:

// wrong
if (true)
    return true;

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

// correct
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:

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:

// wrong
#include <QtCore/QString>

// correct
#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:

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'`

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

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'`

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:

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:

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

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:

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


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.


This page was last edited on 31 October 2019, at 09:57. Content is available under Creative Commons License SA 4.0 unless otherwise noted.