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/*! \page docblocks Documenting the code

\tableofcontents

This chapter covers two topics:

1. How to put comments in your code such that doxygen incorporates them in

   the documentation it generates. 

   This is further detailed in the \ref specialblock "next section".

2. Ways to structure the contents of a comment block such that the output

   looks good, as explained in section \ref docstructure.

\section specialblock Special comment blocks 

A special comment block is a C or C++ style comment block with some 

additional markings, so doxygen knows it is a piece of structured text that

needs to end up in the generated documentation. The \ref cppblock "next" section

presents the various styles supported by doxygen.

For Python, VHDL, Fortran, and Tcl code there are different commenting 

conventions, which can be found in sections \ref pythonblocks, \ref vhdlblocks, 

\ref fortranblocks, and \ref tclblocks respectively.

\subsection cppblock Comment blocks for C-like languages (C/C++/C#/Objective-C/PHP/Java)

For each entity in the code there are two (or in some cases three) types of descriptions, 

which together form the documentation for that entity; a *brief* description and *detailed*

description, both are optional. For methods and functions there is also a third

type of description, the so called *in body* description, which consists of 

the concatenation of all comment blocks found within the body of the method or function.

Having more than one brief or detailed description is allowed (but not recommended,

as the order in which the descriptions will appear is not specified).

As the name suggest, a brief description is

a short one-liner, whereas the detailed description provides longer, 

more detailed documentation. An "in body" description can also act as a detailed

description or can describe a collection of implementation details.

For the HTML output brief descriptions are also

used to provide tooltips at places where an item is referenced.

There are several ways to mark a comment block as a detailed description:

 You can use the JavaDoc style, which consist of a C-style comment

block starting with two *'s, like this:

\verbatim

/**

 * ... text ...

 */

\endverbatim

 or you can use the Qt style and add an exclamation mark (!) 

after the opening of a C-style comment block, as shown in this example:

\verbatim

/*!

 * ... text ...

 */

\endverbatim

In both cases the intermediate *'s are optional, so

\verbatim

/*!

 ... text ...

*/

\endverbatim

is also valid.

 A third alternative is to use a block of at least two C++ comment 

lines, where each line starts with an additional slash or an 

exclamation mark. Here are examples of the two cases:

\verbatim

///

/// ... text ...

///

\endverbatim

or

\verbatim

//!

//!... text ...

//!

\endverbatim

Note that a blank line ends a documentation block in this case.

Some people like to make their comment blocks more visible in the

documentation. For this purpose you can use the following:

\verbatim

/********************************************//**

 *  ... text

 ***********************************************/

\endverbatim

(note the 2 slashes to end the normal comment block and start a special comment block).

or

\verbatim

/////////////////////////////////////////////////

/// ... text ...

/////////////////////////////////////////////////

\endverbatim

For the brief description there are also several possibilities:

One could use the \ref cmdbrief "\\brief" command with one of the 

above comment blocks. This command ends at the end of a paragraph, 

so the detailed description follows after an empty line.

Here is an example:

\verbatim

/*! \brief Brief description.

 *         Brief description continued.

 *

 *  Detailed description starts here.

 */

\endverbatim

If \ref cfg_javadoc_autobrief "JAVADOC_AUTOBRIEF" is set to \c YES 

    in the configuration file, 

    then using JavaDoc style comment

    blocks will automatically start a brief description which ends at the

    first dot followed by a space or new line. Here is an example:

\verbatim

/** Brief description which ends at this dot. Details follow

 *  here.

 */

\endverbatim

The option has the same effect for multi-line special C++ comments:

\verbatim

/// Brief description which ends at this dot. Details follow

/// here.

\endverbatim

A third option is to use a special C++ style comment which does not 

    span more than one line. Here are two examples:

\verbatim

/// Brief description.

/** Detailed description. */

\endverbatim

or

\verbatim

//! Brief description.

//! Detailed description 

//! starts here.

\endverbatim

Note the blank line in the last example, which is required to separate the 

brief description from the block containing the detailed description. The

\ref cfg_javadoc_autobrief "JAVADOC_AUTOBRIEF" should also be set to \c NO

for this case.

As you can see doxygen is quite flexible. If you have multiple

detailed descriptions, like in the following example:

\verbatim

//! Brief description, which is

//! really a detailed description since it spans multiple lines.

/*! Another detailed description!

 */

\endverbatim

They will be joined. Note that this is also the case if the descriptions

are at different places in the code! In this case the order will depend

on the order in which doxygen parses the code.

Unlike most other documentation systems, doxygen also allows you to put

the documentation of members (including global functions) in front of 

the \e definition. This way the documentation can be placed in the source 

file instead of the header file. This keeps the header file compact, and allows the 

implementer of the members more direct access to the documentation.

As a compromise the brief description could be placed before the

declaration and the detailed description before the member definition.

\subsubsection memberdoc Putting documentation after members 

If you want to document the members of a file, struct, union, class, or enum,

it is sometimes desired to place the documentation block after the member 

instead of before. For this purpose you have to put an additional \< marker

in the comment block. Note that this also works for the parameters 

of a function.

Here are some examples:

\verbatim

int var; /*!< Detailed description after the member */

\endverbatim

This block can be used to put a Qt style detailed 

documentation block \e after a member. Other ways to do the

same are:

\verbatim

int var; /**< Detailed description after the member */

\endverbatim

or 

\verbatim

int var; //!< Detailed description after the member

         //!< 

\endverbatim

or 

\verbatim

int var; ///< Detailed description after the member

         ///< 

\endverbatim

Most often one only wants to put a brief description after a member.

This is done as follows:

\verbatim

int var; //!< Brief description after the member

\endverbatim

or

\verbatim

int var; ///< Brief description after the member

\endverbatim

For functions one can use the \ref cmdparam "\@param" command to document the parameters

and then use [in], [out], [in,out] 

to document the direction. For inline documentation this is also possible 

by starting with the direction attribute, e.g.

\verbatim

void foo(int v /**< [in] docs for input parameter v. */);

\endverbatim

Note that these blocks have the same structure and meaning as the 

special comment blocks in the previous section 

only the \< indicates that the member is 

located in front of the block instead of after the block.

Here is an example of the use of these comment blocks:

\include afterdoc.h

 \htmlonly

 Click here

 for the corresponding HTML documentation that is generated by doxygen.

 \endhtmlonly

 \latexonly

 See \hyperlink{afterdoc_example}{After Block example}

 for the corresponding \mbox{\LaTeX} documentation that is generated by doxygen.

 \endlatexonly

\warning These blocks can only be used to document \e members and \e parameters.

         They cannot be used to document files, classes, unions, structs,

         groups, namespaces and enums themselves. Furthermore, the structural 

         commands mentioned in the next section 

         (like \\class) are not allowed 

         inside these comment blocks.

\subsubsection docexamples Examples

Here is an example of a documented piece of C++ code using the Qt style:

\include qtstyle.cpp

 \htmlonly

 Click here

 for the corresponding HTML documentation that is generated by doxygen.

 \endhtmlonly

 \latexonly

 See \hyperlink{qtstyle_example}{QT Style example}

 for the corresponding \mbox{\LaTeX} documentation that is generated by doxygen.

 \endlatexonly

The brief descriptions are included in the member overview of a 

class, namespace or file and are printed using a small italic font 

(this description can be hidden by setting 

\ref cfg_brief_member_desc "BRIEF_MEMBER_DESC" to \c NO in 

the config file). By default the brief descriptions become the first 

sentence of the detailed descriptions 

(but this can be changed by setting the \ref cfg_repeat_brief "REPEAT_BRIEF" 

tag to \c NO). Both the brief and the detailed descriptions are optional 

for the Qt style. 

By default a JavaDoc style documentation block behaves the same way as a

Qt style documentation block. This is not according the JavaDoc specification

however, where the first sentence of the documentation block is automatically

treated as a brief description. To enable this behavior you should set

\ref cfg_javadoc_autobrief "JAVADOC_AUTOBRIEF" to YES in the configuration

file. If you enable this option and want to put a dot in the middle of a

sentence without ending it, you should put a backslash and a space after it.

Here is an example:

\verbatim

  /** Brief description (e.g.\ using only a few words). Details follow. */

\endverbatim

Here is the same piece of code as shown above, this time documented using the 

JavaDoc style and \ref cfg_javadoc_autobrief "JAVADOC_AUTOBRIEF" set to YES:

\include jdstyle.cpp

 \htmlonly

 Click here

 for the corresponding HTML documentation that is generated by doxygen.

 \endhtmlonly

 \latexonly

 See \hyperlink{jdstyle_example}{Javadoc Style example}

 for the corresponding \mbox{\LaTeX} documentation that is generated by doxygen.

 \endlatexonly

Similarly, if one wishes the first sentence of a Qt style documentation

block to automatically be treated as a brief description, one may set

\ref cfg_qt_autobrief "QT_AUTOBRIEF" to YES in the configuration file.

\subsubsection structuralcommands Documentation at other places

In the examples in the previous section the comment blocks were always located *in 

front* of the declaration or definition of a file, class or namespace or *in

front* or *after* one of its members. 

Although this is often comfortable, there may sometimes be reasons to put the 

documentation somewhere else. For documenting a file this is even 

required since there is no such thing as "in front of a file". 

Doxygen allows you to put your documentation blocks practically 

anywhere (the exception is inside the body of a function or inside a 

normal C style comment block). 

The price you pay for not putting the

documentation block directly before (or after) an item is the need to put a  

structural command inside the documentation block, which leads to some

duplication of information. So in practice you should \e avoid the use of

structural commands \e unless other requirements force you to do so.

Structural commands (like \ref cmd_intro "all other commands") start with a backslash 

(<tt>\\</tt>), or an at-sign (<tt>\@</tt>) if you prefer JavaDoc style, 

followed by a command name and one or more parameters.

For instance, if you want to document the class \c Test in the example

above, you could have also put the following documentation block somewhere

in the input that is read by doxygen:

\verbatim

/*! \class Test

    \brief A test class.

    A more detailed class description.

*/

\endverbatim

Here the special command \c \\class is used to indicate that the

comment block contains documentation for the class \c Test.

Other structural commands are:

\c \\struct to document a C-struct.

\c \\union to document a union.

\c \\enum to document an enumeration type.

\c \\fn to document a function.

\c \\var to document a variable or typedef or enum value.

\c \\def to document a \#define.

\c \\typedef to document a type definition.

\c \\file to document a file.

\c \\namespace to document a namespace.

\c \\package to document a Java package.

\c \\interface to document an IDL interface.

See section \ref commands for detailed information about these and many other 

commands. 

To document a member of a C++ class, you must also document the class 

itself. The same holds for namespaces. To document a global C function, 

typedef, enum or preprocessor definition you must first document the file 

that contains it (usually this will be a header file, because that file 

contains the information that is exported to other source files).

@attention Let's repeat that, because it is often overlooked:

to document global objects (functions, typedefs, enum, macros, etc), you

must document the file in which they are defined. In other words, 

there must at least be a \verbatim /*! \file */ \endverbatim

or a \verbatim /** @file */ \endverbatim line in this file.

Here is an example of a C header named \c structcmd.h that is documented 

using structural commands:

\include structcmd.h

 \htmlonly

 Click here

 for the corresponding HTML documentation that is generated by doxygen.

 \endhtmlonly

 \latexonly

 See \hyperlink{structcmd_example}{Structural Commands example}

 for the corresponding \mbox{\LaTeX} documentation that is generated by doxygen.

 \endlatexonly

 Because each comment block in the example above contains a structural command, all

 the comment blocks could be moved to another location or input file 

 (the source file for instance), without affecting the generated 

 documentation. The disadvantage of this approach is that prototypes are

 duplicated, so all changes have to be made twice! Because of this you

 should first consider if this is really needed, and avoid structural

 commands if possible. I often receive examples that contain \\fn command

 in comment blocks which are place in front of a function. This is clearly

 a case where the \\fn command is redundant and will only lead to problems.

 When you place a comment block in a file with one of the following extensions

 `.dox`, `.txt`, or `.doc` then doxygen will hide this file from the file list.

 If you have a file that doxygen cannot parse but still would like to document it,

 you can show it as-is using \ref cmdverbinclude "\\verbinclude", e.g.

\verbatim

/*! \file myscript.sh

 *  Look at this nice script:

 *  \verbinclude myscript.sh

 */

\endverbatim

Make sure that the script is explicitly listed in the \ref cfg_input "INPUT" or

that \ref cfg_file_patterns "FILE_PATTERNS" includes the `.sh` extension and the

the script can be found in the path set via \ref cfg_example_path "EXAMPLE_PATH".

\subsection pythonblocks Comment blocks in Python

For Python there is a standard way of documenting the code using 

so called documentation strings. Such strings are stored in \c __doc__

and can be retrieved at runtime. Doxygen will extract such comments

and assume they have to be represented in a preformatted way.

\include docstring.py

 \htmlonly

 Click here

 for the corresponding HTML documentation that is generated by doxygen.

 \endhtmlonly

 \latexonly

 See \hyperlink{python_example}{Python Docstring example}

 for the corresponding \mbox{\LaTeX} documentation that is generated by doxygen.

 \endlatexonly

Note that in this case none of doxygen's \ref cmd_intro "special commands" 

are supported.

There is also another way to document Python code using comments that 

start with "##". These type of comment blocks are more in line with the 

way documentation blocks work for the other languages supported by doxygen 

and this also allows the use of special commands. 

Here is the same example again but now using doxygen style comments:

\include pyexample.py

 \htmlonly

 Click here

 for the corresponding HTML documentation that is generated by doxygen.

 \endhtmlonly

 \latexonly

 See \hyperlink{py_example}{Python example}

 for the corresponding \mbox{\LaTeX} documentation that is generated by doxygen.

 \endlatexonly

Since python looks more like Java than like C or C++, you should set 

\ref cfg_optimize_output_java "OPTIMIZE_OUTPUT_JAVA" to \c YES in the

config file. 

\subsection vhdlblocks Comment blocks in VHDL

For VHDL a comment normally start with "--". Doxygen will extract comments

starting with "--!". There are only two types of comment blocks in VHDL;

a one line "--!" comment representing a brief description, and a multi-line

"--!" comment (where the "--!" prefix is repeated for each line) representing

a detailed description.

Comments are always located in front of the item that is being documented

with one exception: for ports the comment can also be after the item

and is then treated as a brief description for the port.

Here is an example VHDL file with doxygen comments:

\include  mux.vhdl

 \htmlonly

 Click here

 for the corresponding HTML documentation that is generated by doxygen.

 \endhtmlonly

 \latexonly

 See \hyperlink{vhdl_example}{VHDL example}

 for the corresponding \mbox{\LaTeX} documentation that is generated by doxygen.

 \endlatexonly

To get proper looking output you need to set

\ref cfg_optimize_output_vhdl "OPTIMIZE_OUTPUT_VHDL" to \c YES in the

config file. This will also affect a number of other settings. When they

were not already set correctly doxygen will produce a warning telling which

settings where overruled.

\subsection fortranblocks Comment blocks in Fortran

When using doxygen for Fortran code you should

set \ref cfg_optimize_for_fortran "OPTIMIZE_FOR_FORTRAN" to \c YES.

The parser tries to guess if the source code is fixed format Fortran or

free format Fortran code. This may not always be correct. If not

one should use \ref cfg_extension_mapping "EXTENSION_MAPPING" to correct this.

By setting `EXTENSION_MAPPING =  f=FortranFixed f90=FortranFree` files with

extension \c f are interpreted as fixed format Fortran code and files with

extension \c f90 are interpreted as free format Fortran code.

For Fortran "!>" or "!<" starts a comment and "!!" or "!>" can be used to 

continue an one line comment into a multi-line comment.

Here is an example of a documented Fortran subroutine:

\code{.f}

  !> Build the restriction matrix for the aggregation 

  !! method.

  !! @param aggr information about the aggregates

  !! @todo Handle special case

  subroutine IntRestBuild(A,aggr,Restrict,A_ghost)

    implicit none

    Type(SpMtx), intent(in) :: A !< our fine level matrix

    Type(Aggrs), intent(in) :: aggr

    Type(SpMtx), intent(out) :: Restrict !< Our restriction matrix

    !...

  end subroutine

\endcode

As an alternative you can also use comments in fixed format code:

\code{.f}

C> Function comment

C> another line of comment

      function A(i)

C> input parameter

        integer i

      end function A

\endcode

\subsection tclblocks Comment blocks in Tcl

Doxygen documentation can be included in normal Tcl comments.

To start a new documentation block start a line with \c ## (two hashes).

All following comment lines and continuation lines will be added to this

block. The block ends with a line not starting with a \c # (hash sign).

A brief documentation can be added with \c ;#< (semicolon, hash and

lower then sign). The brief documentation also ends at a line not starting

with a \c # (hash sign).

Inside doxygen comment blocks all normal doxygen markings are supported.

The only exceptions are described in the following two paragraphs.

If a doxygen comment block ends with a line containing only

\c #\\code or \c #\@code all code until a line only containing \c #\\endcode

or \c #\@endcode is added to the generated documentation as code block.

If a doxygen comment block ends with a line containing only

\c #\\verbatim or \c #\@verbatim all code until a line only containing

\c #\\endverbatim or \c #\@endverbatim is added verbatim to the generated

documentation.

To detect namespaces, classes, functions and variables the following

Tcl commands are recognized. Documentation blocks can be put on the lines

before the command.

<tt>namespace eval ..</tt> Namespace

<tt>proc ..</tt> Function

<tt>variable ..</tt> Variable

<tt>common ..</tt> Common variable

<tt>itcl::class ..</tt> Class

<tt>itcl::body ..</tt> Class method body definition

<tt>oo::class create ..</tt> Class

<tt>oo::define ..</tt> OO Class definition

<tt>method ..</tt> Class method definitions

<tt>constructor ..</tt> Class constructor

<tt>destructor ..</tt> Class destructor

<tt>public ..</tt> Set protection level

<tt>protected ..</tt> Set protection level

<tt>private ..</tt> Set protection level

To use your own keywords you an map these keyword to the recognized commands

using the \ref cfg_tcl_subs "TCL_SUBST" entry in the config file.

The entry contain a list of word-keyword mappings. To use the itcl::*

commands without the leading namespace use p.e.:

\verbatim TCL_SUBST = class itcl:class body itcl:body \endverbatim

-->

Following is an example using doxygen style comments:

\include tclexample.tcl

 \htmlonly

 Click here

 for the corresponding HTML documentation that is generated by doxygen.

 \endhtmlonly

 \latexonly

 See \hyperlink{tcl_example}{TCL example}

 for the corresponding \mbox{\LaTeX} documentation that is generated by doxygen.

 \endlatexonly

\section docstructure Anatomy of a comment block

The previous section focused on how to make the comments in your code known

to doxygen, it explained the difference between a brief and a detailed description, and

the use of structural commands.

In this section we look at the contents of the comment block itself.

Doxygen supports various styles of formatting your comments.

The simplest form is to use plain text. This will appear as-is in the output 

and is ideal for a short description.

For longer descriptions you often will find the 

need for some more structure, like a block of verbatim text, a list, or a 

simple table. For this doxygen supports the 

Markdown 

syntax, including parts of the

Markdown Extra

extension. 

Markdown is designed to be very easy to read and write. 

It's formatting is inspired by plain text mail.

Markdown works great for simple, generic formatting, like an introduction

page for your project. Doxygen also supports reading of markdown files 

directly. For more details see chapter \ref markdown.

For programming language specific formatting doxygen has two

forms of additional markup on top of Markdown formatting.

1. Javadoc like markup.

   See \ref commands for a complete overview of all commands supported by doxygen.

2. XML markup

   as specified in the C# standard. See \ref xmlcmds for the XML commands supported by doxygen.

If this is still not enough doxygen also supports a \ref htmlcmds "subset" of 

the HTML markup language.

\htmlonly

Go to the next section or return to the

 index.

\endhtmlonly

*/