####################
Documenting C++ Code
####################
.. note::
This is a preview documentation format specification.
Software documentation should currently be written in the format described at https://confluence.lsstcorp.org/display/LDMDG/Documentation+Standards
The LSST Stack uses `Doxygen `_ to build C++ API reference documentation by extracting source code comments.
This page covers the most important concepts in writing Doxygen-friendly C++ comments for the LSST Stack, though `Doxygen's manual `_ is the most comprehensive reference.
Note that LSST uses `Markdown-formatted Doxygen comment blocks `_.
This document is ported from original documentation in Confluence; https://confluence.lsstcorp.org/display/LDMDG/Documentation+Standards.
**This guide will evolve as a mechanism to document C++ APIs wrapped in Python in developed.**
Boilerplate for Header (.h) and Source (.cpp) Files
===================================================
The beginning of both header and source code files should include
1. A formating hint for Emacs
.. code-block:: cpp
// -*- lsst-c++ -*-
2. A copyright and license block
.. code-block:: cpp
/*
* LSST Data Management System
* See COPYRIGHT file at the top of the source tree.
*
* This product includes software developed by the
* LSST Project (http://www.lsst.org/).
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the LSST License Statement and
* the GNU General Public License along with this program. If not,
* see .
*/
File Description Comment for Header Files
=========================================
After the boilerplate, any C++ header file should have a Doxygen-style comment block (that begins with ``/**``) that includes the following fields:
1. ``@file`` giving the file's name
2. ``@brief`` to provide a synopsis of the file for Doxygen's index. This should be a line, at most.
3. ``@ingroup`` to specify the name of the LSST Stack package containing this file (see :ref:`below `).
4. ``@author`` to provide the name of the file's primary author.
For example:
.. code-block:: cpp
/**
* @file ExampleClass.cc
*
* @brief This message displayed in Doxygen Files index
*
* @ingroup PackageName
* (Note: this needs exactly one @defgroup somewhere)
*
* @author Joe Smith
* Contact: js@lsst.org
*
*/
.. _doc-cpp-package-definition:
Package Documentation / Definition
==================================
Each LSST package corresponds to a group in Doxygen.
We declare this package in the root header file for a package, usually named ``package.h``.
In this header file, below the preamble, provide a Doxygen comment block that declares the package with the fields:
1. ``@defgroup`` followed by the ``PackageName`` and ``PackageTitle``
2. ``@brief`` to provide a one-line description of the package.
For example:
.. code-block:: cpp
/**
* @defgroup PackageName PackageTitle
*
* @brief Provide some stuff to do stuff
*/
Class Definitions
=================
Where a class is *defined* (usually in a header file), provide a Doxygen block preceeding the class that includes
1. A one-line description of the class.
2. A paragraph (or more) describing the class. Markdown can be used to provide nuanced typography.
For example:
.. code-block:: cpp
/**
* Implementation of a trace facility for LSST
*
* Tracing is controlled on a per "component" basis, where a "component" is a
* name of the form aaa.bbb.ccc where aaa is the Most significant part; for
* example, the utilities library might be called "utils", the doubly-linked
* list "utils.dlist", and the code to destroy a list "utils.dlist.del"
*
*/
class TraceImpl {
public:
}
Function/Method Definitions
===========================
Where a function or class method is *defined*, provide a Doxygen block preceeding that class that includes
1. A one-line description of the function/method
2. Optionally, a paragraph or more with detailed descriptions of the function/method. Markdown can be used here.
3. ``@param`` statements describing each function/method argument. Optionally, inline comments can be used (see below).
An example of a Doxygen comment for a function:
.. code-block:: cpp
/** Set a component's verbosity.
*
* If no verbosity is specified, inherit from parent
*
* @param name component of interest
* @param verbosity desired trace verbosity
*/
void TraceImpl::setVerbosity(const std::string &name, const int verbosity) {
}
Annotating Arguments with Inline Comments (optional)
----------------------------------------------------
If the argument descriptions are very short, you may choose to annotate arguments with inline comments after each argument, one per line.
These comments are prefixed with ``///< set:``.
For example:
.. code-block:: cpp
/** Set a component's verbosity.
*
* If no verbosity is specified, inherit from parent
*/
void TraceImpl::setVerbosity(const std::string &name, ///< component of interest
const int verbosity) { ///< desired trace verbosity
}
If the argument descriptions are too long to fit in a single line of source, the ``@param`` documenation method should be used.
Overloaded Function/Methods Definitions
=======================================
'`@overload`` may be used when two methods/functions are effectively the same but have different parameters list for reasons of convenience.
For example:
.. code-block:: cpp
/**
* seconds from midnight
*/
long GetTime(void){
return secondFromMidnight(CURRENT);
}
/**
# @overload void GetTime(int &hours, int &minutes, int &seconds)
*/
void GetTime(int &hours, ///< set: current hour
int &minutes, ///< set: current minutes
int &seconds) { ///< set: current seconds
hours = _hours;
minutes = _minutes;
seconds = _seconds;
}