Keywords: ISO C++ , library

Documentation Style
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## Documentation Style

### Doxygen

#### Prerequisites

Prerequisite tools are Bash 2.x, Doxygen, and the GNU coreutils. (GNU versions of find, xargs, and possibly sed and grep are used, just because the GNU versions make things very easy.)

To generate the pretty pictures and hierarchy graphs, the Graphviz package will need to be installed.

#### Generating the Doxygen Files

The following Makefile rules run Doxygen to generate HTML docs, XML docs, and the man pages.

    make doc-html-doxygen

    make doc-xml-doxygen

    make doc-man-doxygen

Careful observers will see that the Makefile rules simply call a script from the source tree, `run_doxygen`, which does the actual work of running Doxygen and then (most importantly) massaging the output files. If for some reason you prefer to not go through the Makefile, you can call this script directly. (Start by passing `--help`.)

If you wish to tweak the Doxygen settings, do so by editing `doc/doxygen/user.cfg.in`. Notes to fellow library hackers are written in triple-# comments.

#### Markup

In general, libstdc++ files should be formatted according to the rules found in the Coding Standard. Before any doxygen-specific formatting tweaks are made, please try to make sure that the initial formatting is sound.

Adding Doxygen markup to a file (informally called “doxygenating”) is very simple. The Doxygen manual can be found here. We try to use a very-recent version of Doxygen.

For classes, use `deque`/`vector`/`list` and `std::pair` as examples. For functions, see their member functions, and the free functions in `stl_algobase.h`. Member functions of other container-like types should read similarly to these member functions.

Some commentary to accompany the first list in the Special Documentation Blocks section of the Doxygen manual:

1. For longer comments, use the Javadoc style...

2. ...not the Qt style. The intermediate *'s are preferred.

3. Use the triple-slash style only for one-line comments (the “brief” mode).

4. This is disgusting. Don't do this.

Some specific guidelines:

Use the @-style of commands, not the !-style. Please be careful about whitespace in your markup comments. Most of the time it doesn't matter; doxygen absorbs most whitespace, and both HTML and *roff are agnostic about whitespace. However, in <pre> blocks and @code/@endcode sections, spacing can have “interesting” effects.

Use either kind of grouping, as appropriate. `doxygroups.cc` exists for this purpose. See `stl_iterator.h` for a good example of the “other” kind of grouping.

Please use markup tags like @p and @a when referring to things such as the names of function parameters. Use @e for emphasis when necessary. Use @c to refer to other standard names. (Examples of all these abound in the present code.)

Complicated math functions should use the multi-line format. An example from `random.h`:

/**
* @brief A model of a linear congruential random number generator.
*
* @f[
* x_{i+1}\leftarrow(ax_{i} + c) \bmod m
* @f]
*/

Be careful about using certain, special characters when writing Doxygen comments. Single and double quotes, and separators in filenames are two common trouble spots. When in doubt, consult the following table.

Table A.1. HTML to Doxygen markup comparison

HTML | Doxygen
--- | ---
\ | \\
" | \"
' | \'
<i> | @a word
<b> | @b word
<code> | @c word
<em> | @a word
<em> | <em>two words or more</em>

### Docbook

#### Prerequisites

Editing the DocBook sources requires an XML editor. Many exist: some notable options include emacs, Kate, or Conglomerate.

Some editors support special “XML Validation” modes that can validate the file as it is produced. Recommended is the nXML Mode for emacs.

Besides an editor, additional DocBook files and XML tools are also required.

Access to the DocBook stylesheets and DTD is required. The stylesheets are usually packaged by vendor, in something like `docbook-style-xsl`. To exactly match generated output, please use a version of the stylesheets equivalent to `docbook-style-xsl-1.74.0-5`. The installation directory for this package corresponds to the `XSL_STYLE_DIR` in `doc/Makefile.am` and defaults to `/usr/share/sgml/docbook/xsl-stylesheets`.

For processing XML, an XML processor and some style sheets are necessary. Defaults are xsltproc provided by `libxslt`.

For validating the XML document, you'll need something like xmllint and access to the DocBook DTD. These are provided by a vendor package like `libxml2`.

For PDF output, something that transforms valid XML to PDF is required. Possible solutions include xmlto, Apache FOP, or prince. Other options are listed on the DocBook web pages. Please consult the `<libstdc++@gcc.gnu.org>` list when preparing printed manuals for current best practice and suggestions.

Make sure that the XML documentation and markup is valid for any change. This can be done easily, with the validation rules in the `Makefile`, which is equivalent to doing:

    xmllint --noout --valid xml/index.xml

#### Generating the DocBook Files

The following Makefile rules generate (in order): an HTML version of all the documentation, a PDF version of the same, a single XML document, and the result of validating the entire XML document.

    make doc-html

    make doc-pdf

    make doc-xml-single

    make doc-xml-validate

#### File Organization and Basics

Which files are important
All Docbook files are in the directory
libstdc++-v3/doc/xml
Inside this directory, the files of importance:
spine.xml - index to documentation set
manual/spine.xml - index to manual
manual/*.xml - individual chapters and sections of the manual
faq.xml - index to FAQ
api.xml - index to source level / API
All *.txml files are template xml files, i.e., otherwise empty files with
the correct structure, suitable for filling in with new information.
Canonical Writing Style
class template
function template
member function template
(via C++ Templates, Vandevoorde)
class in namespace std: allocator, not std::allocator
header file: iostream, not <iostream>
General structure
<set>
<book>
</book>
<book>
<chapter>
</chapter>
</book>
<book>
<part>
<chapter>
<section>
</section>
<sect1>
</sect1>
<sect1>
<sect2>
</sect2>
</sect1>
</chapter>
<chapter>
</chapter>
</part>
</book>
</set>

#### Markup By Example

Complete details on Docbook markup can be found in the DocBook Element Reference, online. An incomplete reference for HTML to Docbook conversion is detailed in the table below.

Table A.2. HTML to Docbook XML markup comparison

HTML | Docbook
--- | ---
<p> | <para>
<pre> | <computeroutput>, <programlisting>, <literallayout>
<ul> | <itemizedlist>
<ol> | <orderedlist>
<il> | <listitem>
<dl> | <variablelist>
<dt> | <term>
<dd> | <listitem>
<a href=""> | <ulink url="">
<code> | <literal>, <programlisting>
<strong> | <emphasis>
<em> | <emphasis>
" | <quote>

And examples of detailed markup for which there are no real HTML equivalents are listed in the table below.

Table A.3. Docbook XML Element Use

Element | Use
--- | ---
<structname> | <structname>char_traits</structname>
<classname> | <classname>string</classname>
<function> | <function>clear()</function> <function>fs.clear()</function>
<type> | <type>long long</type>
<varname> | <varname>fs</varname>
<literal> | <literal>-Weffc++</literal> <literal>rel_ops</literal>
<constant> | <constant>_GNU_SOURCE</constant> <constant>3.0</constant>
<command> | <command>g++</command>
<errortext> | <errortext>In instantiation of</errortext>
<filename> | <filename class="headerfile">ctype.h</filename> <filename class="directory">/home/gcc/build</filename> <filename class="libraryfile">libstdc++.so</filename>

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