Creating Documentation

ns-3 supplies two kinds of documentation: expository “user-guide”-style chapters, and source code API documentation.

The “user-guide” chapters are written by hand in reStructuredText format (.rst), which is processed by the Python documentation system Sphinx to generate web pages and pdf files. The API documentation is generated from the source code itself, using Doxygen, to generate cross-linked web pages. Both of these are important: the Sphinx chapters explain the why and overview of using a model; the API documentation explains the how details.

This chapter gives a quick overview of these tools, emphasizing preferred usage and customizations for ns-3.

To build all the standard documentation:

$ ./ns3 docs

For more specialized options, read on.

Documenting with Sphinx

We use Sphinx to generate expository chapters describing the design and usage of each module. Right now you are reading the Documentation Chapter. If you are reading the html version, the Show Source link in the sidebar will show you the reStructuredText source for this chapter.

Adding New Chapters

Adding a new chapter takes three steps (described in more detail below):

  1. Choose Where? the documentation file(s) will live.
  2. Link from an existing page to the new documentation.
  3. Add the new file to the Makefile.


Documentation for a specific module, foo, should normally go in src/foo/doc/. For example src/foo/doc/foo.rst would be the top-level document for the module. The utils/ script will create this file for you.

Some models require several .rst files, and figures; these should all go in the src/foo/doc/ directory. The docs are actually built by a Sphinx Makefile. For especially involved documentation, it may be helpful to have a local Makefile in the src/foo/doc/ directory to simplify building the documentation for this module (Antenna is an example). Setting this up is not particularly hard, but is beyond the scope of this chapter.

In some cases, documentation spans multiple models; the Network chapter is an example. In these cases adding the .rst files directly to doc/models/source/ might be appropriate.


You also have to add your document to the appropriate Makefile, so make knows to check it for updates. The Models book Makefile is doc/models/Makefile, the Manual book Makefile is doc/manual/Makefile.

# list all model library .rst files that need to be copied to $SOURCETEMP
        source/ \
        source/_static \
        source/index.rst \
        source/replace.txt \
        source/organization.rst \
        $(SRC)/antenna/doc/source/antenna.rst \

You add your .rst files to the SOURCES variable. To add figures, read the comments in the Makefile to see which variable should contain your image files. Again, please keep these in alphabetical order.

Building Sphinx Docs

Building the Sphinx documentation is pretty simple. To build all the Sphinx documentation:

$ ./ns3 sphinx

To build just the Models documentation:

$ make -C doc/models html

To see the generated documentation point your browser at doc/models/build/html.

As you can see, Sphinx uses Make to guide the process. The default target builds all enabled output forms, which in ns-3 are the multi-page html, single-page singlehtml, and pdf (latex). To build just the multi-page html, you add the html target:

$ make -C doc/models html

This can be helpful to reduce the build time (and the size of the build chatter) as you are writing your chapter.

Before committing your documentation to the repo, please check that it builds without errors or warnings. The build process generates lots of output (mostly normal chatter from LaTeX), which can make it difficult to see if there are any Sphinx warnings or errors. To find important warnings and errors build just the html version, then search the build log for warning or error.

ns-3 Specifics

The Sphinx documentation and tutorial are pretty good. We won’t duplicate the basics here, instead focusing on preferred usage for ns-3.

  • Start documents with these two lines:

    .. include:: replace.txt
    .. highlight:: cpp

    The first line enables some simple replacements. For example, typing |ns3| renders as ns-3. The second sets the default source code highlighting language explicitly for the file, since the parser guess isn’t always accurate. (It’s also possible to set the language explicitly for a single code block, see below.)

  • Sections:

    Sphinx is pretty liberal about marking section headings. By convention, we prefer this hierarchy:

    .. heading hierarchy:
       ------------- Chapter
       ************* Section (#.#)
       ============= Subsection (#.#.#)
       ############# Sub-subsection
  • Syntax Highlighting:

    To use the default syntax highlighter, simply start a sourcecode block:

    Sphinx Source Rendered Output
    The ``Frobnitz`` is accessed by::
      Foo::Frobnitz frob;
      frob.Set (...);

    The Frobnitz is accessed by:

    Foo::Frobnitz frob;
    frob.Set (...);

    To use a specific syntax highlighter, for example, bash shell commands:

    Sphinx Source Rendered Output
    .. sourcecode:: bash
       $ ls
    $ ls
  • Shorthand Notations:

    These shorthands are defined:

    Sphinx Source Rendered Output
    RFC 6282

Documenting with Doxygen

We use Doxygen to generate browsable API documentation. Doxygen provides a number of useful features:

  • Summary table of all class members.
  • Graphs of inheritance and collaboration for all classes.
  • Links to the source code implementing each function.
  • Links to every place a member is used.
  • Links to every object used in implementing a function.
  • Grouping of related classes, such as all the classes related to a specific protocol.

In addition, we use the TypeId system to add to the documentation for every class

  • The Config paths by which such objects can be reached.
  • Documentation for any Attributes, including Attributes defined in parent classes.
  • Documentation for any Trace sources defined by the class.
  • The memory footprint for each class.

Doxygen operates by scanning the source code, looking for specially marked comments. It also creates a cross reference, indicating where each file, class, method, and variable is used.

Preferred Style

The preferred style for Doxygen comments is the JavaDoc style:

 *  Brief description of this class or method.
 *  Adjacent lines become a single paragraph.
 *  Longer description, with lots of details.
 *  Blank lines separate paragraphs.
 *  Explain what the class or method does, using what algorithm.
 *  Explain the units of arguments and return values.
 *  \note Note any limitations or gotchas.
 *  (For functions with arguments or return valued:)
 *  \param [in] foo Brief noun phrase describing this argument. Note
 *                  that we indicate if the argument is input,
 *                  output, or both.
 *  \param [in,out] bar Note Sentence case, and terminating period.
 *  \param [in] baz Indicate boolean values with \c true or \c false.
 *  \return Brief noun phrase describing the value.
 *  \internal
 *  You can also discuss internal implementation details.
 *  Understanding this material shouldn't be necessary to using
 *  the class or method.
 void ExampleFunction (const int foo, double & bar, const bool baz);

In this style the Doxygen comment block begins with two `*’ characters: /**, and precedes the item being documented.

For items needing only a brief description, either of these short forms is appropriate:

/** Destructor implementation. */
void DoDispose ();

int m_count;  //!< Count of ...

Note the special form of the end of line comment, //!<, indicating that it refers to the preceding item.

Some items to note:

  • Use sentence case, including the initial capital.
  • Use punctuation, especially `.’s at the end of sentences or phrases.
  • The \brief tag is not needed; the first sentence will be
    used as the brief description.

Every class, method, typedef, member variable, function argument and return value should be documented in all source code files which form the formal API and implementation for ns-3, such as src/<module>/model/*, src/<module>/helper/* and src/<module>/utils/*. Documentation for items in src/<module>/test/* and src/<module>/examples/* is preferred, but not required.

Useful Features

  • Inherited members will automatically inherit docs from the parent, (but can be replaced by local documentation).

    1. Document the base class.

    2. In the sub class mark inherited functions with an ordinary comment:

      // Inherited methods
      virtual void FooBar (void);
      virtual int BarFoo (double baz);

      Note that the signatures have to match exactly, so include the formal argument (void)

      This doesn’t work for static functions; see GetTypeId, below, for an example.

Building Doxygen Docs

Building the Doxygen documentation is pretty simple:

$ ./ns3 doxygen

This builds using the default configuration, which generates documentation sections for all items, even if they do not have explicit comment documentation blocks. This has the effect of suppressing warnings for undocumented items, but makes sure everything appears in the generated output, which is usually what you want for general use. Note that we generate documentation even for modules which are disabled, to make it easier to see all the features available in ns-3.

When writing documentation, it’s often more useful to see which items are generating warnings, typically about missing documentation. To see the full warnings list, use the doc/ script:

$ doc/
Building and running print-introspected-doxygen...done.
Rebuilding doxygen (v1.8.10) docs with full errors...done.

Report of Doxygen warnings

(All counts are lower bounds.)

Warnings by module/directory:

Count Directory
----- ----------------------------------
3414 src/lte/model
1532 src/wimax/model
 825 src/lte/test
   1 src/applications/test
 97 additional undocumented parameters.
 12460 total warnings
   100 directories with warnings

Warnings by file (alphabetical)

Count File
----- ----------------------------------
  15 examples/routing/
  26 examples/stats/wifi-example-apps.h
  12 examples/tutorial/
  17 utils/
   771 files with warnings

Warnings by file (numerical)

Count File
----- ----------------------------------
 273 src/lte/model/lte-rrc-sap.h
 272 src/core/model/simulator.h
 221 src/netanim/model/animation-interface.h
   1 src/wimax/model/
   771 files with warnings

Doxygen Warnings Summary
   100 directories
   771 files
 12460 warnings

(This snippet has a lot of lines suppressed!)

The script modifies the configuration to show all warnings, and to shorten the run time. (It shortens the run time primarily by disabling creation of diagrams, such as call trees, and doesn’t generate documentation for undocumented items, in order to trigger the warnings.) As you can see, at this writing we have a lot of undocumented items. The report summarizes warnings by module src/*/*, and by file, in alphabetically and numerical order.

The script has a few options to pare things down and make the output more manageable. For help, use the -h option. Having run it once to do the Doxygen build and generate the full warnings log, you can reprocess the log file with various “filters,” without having to do the full Doxygen build again by using the -s option. You can exclude warnings from */examples/* files (-e option), and/or */test/* files (-t). Just to be clear, all of the filter options do the complete fast doxygen build; they just filter doxygen log and warnings output.

Perhaps the most useful option when writing documentation comments is -m <module>, which will limit the report to just files matching src/<module>/*, and follow the report with the actual warning lines. Combine with -et and you can focus on the warnings that are most urgent in a single module:

$ doc/ -m mesh/helper
Doxygen Warnings Summary
  1 directories
  3 files
149 warnings

Filtered Warnings
src/mesh/helper/dot11s/dot11s-installer.h:72: warning: Member m_root (variable) of class ns3::Dot11sStack is not documented.
src/mesh/helper/dot11s/dot11s-installer.h:35: warning: return type of member ns3::Dot11sStack::GetTypeId is not documented
src/mesh/helper/dot11s/dot11s-installer.h:56: warning: return type of member ns3::Dot11sStack::InstallStack is not documented
src/mesh/helper/flame/lfame-installer.h:40: warning: Member GetTypeId() (function) of class ns3::FlameStack is not documented.
src/mesh/helper/flame/flame-installer.h:60: warning: return type of member ns3::FlameStack::InstallStack is not documented
src/mesh/helper/mesh-helper.h:213: warning: Member m_nInterfaces (variable) of class ns3::MeshHelper is not documented.
src/mesh/helper/mesh-helper.h:214: warning: Member m_spreadChannelPolicy (variable) of class ns3::MeshHelper is not documented.
src/mesh/helper/mesh-helper.h:215: warning: Member m_stack (variable) of class ns3::MeshHelper is not documented.
src/mesh/helper/mesh-helper.h:216: warning: Member m_stackFactory (variable) of class ns3::MeshHelper is not documented.
src/mesh/helper/mesh-helper.h:209: warning: parameters of member ns3::MeshHelper::CreateInterface are not (all) documented
src/mesh/helper/mesh-helper.h:119: warning: parameters of member ns3::MeshHelper::SetStandard are not (all) documented

Finally, note that undocumented items (classes, methods, functions, typedefs, etc. won’t produce documentation when you build with, and only the outermost item will produce a warning. As a result, if you don’t see documentation for a class method in the generated documentation, the class itself probably needs documentation.

Now it’s just a matter of understanding the code, and writing some docs!

ns-3 Specifics

As for Sphinx, the Doxygen docs and reference are pretty good. We won’t duplicate the basics here, instead focusing on preferred usage for ns-3.

  • Use Doxygen Modules to group related items.

    In the main header for a module, create a Doxgyen group:

     *  \defgroup foo Foo protocol.
     *  Implementation of the Foo protocol.

    The symbol foo is how other items can add themselves to this group. The string following that will be the title for the group. Any further text will be the detailed description for the group page.

  • Document each file, assigning it to the relevant group. In a header file:

     *  \file
     *  \ingroup foo
     *  Class Foo declaration.

    or in the corresponding .cc file:

     *  \file
     *  \ingroup foo
     *  Class FooBar implementation.
  • Mark each associated class as belonging to the group:

     *  \ingroup foo
     *  FooBar packet type.
    class FooBar
  • Did you know typedefs can have formal arguments? This enables documentation of function pointer signatures:

     *  Bar callback function signature.
     *  \param ale The size of a pint of ale, in Imperial ounces.
    typedef void (* BarCallback)(const int ale);
  • Copy the Attribute help strings from the GetTypeId method to use as the brief descriptions of associated members.

  • \bugid{298} will create a link to bug 298 in our Bugzilla.

  • \p foo in a description will format foo the same as the \param foo parameter, making it clear that you are referring to an actual argument.

  • \RFC{301} will create a link to RFC 301.

  • Document the direction of function arguments with \param [in], etc. The allowed values of the direction token are [in], [out], and [in,out] (note the explicit square brackets), as discussed in the Doxygen docs for \param.

  • Document template arguments with \tparam, just as you use \param for function arguments.

  • For template arguments, indicate if they will be deduced or must be given explicitly:

     * A templated function.
     * \tparam T \explicit The return type.
     * \tparam U \deduced The argument type.
     * \param [in] a The argument.
    template <typename T, typename U> T Function (U a);
    • Use \tparam U \deduced because the type U can be deduced at the site where the template is invoked. Basically deduction can only be done for function arguments.
    • Use \tparam T \explicit because the type T can’t be deduced; it must be given explicitly at the invocation site, as in Create<MyObject> (...)
  • \internal should be used only to set off a discussion of implementation details, not to mark private functions (they are already marked, as private!)

  • Don’t create classes with trivial names, such as class A, even in test suites. These cause all instances of the class name literal `A’ to be rendered as links.

As noted above, static functions don’t inherit the documentation of the same functions in the parent class. ns-3 uses a few static functions ubiquitously; the suggested documentation block for these cases is:

  • Default constructor/destructor:

    MyClass ();   //!< Default constructor
    ~MyClass ();  //!< Destructor
  • Dummy destructor and DoDispose:

    /** Dummy destructor, see DoDispose. */
    ~MyClass ();
    /** Destructor implementation */
    virtual void DoDispose ();
  • GetTypeId:

     *  Register this type.
     *  \return The object TypeId.
    static TypeId GetTypeId (void);