# Doxygen

Doxygen (/ˈdɒksidʒən/ DOK-see-jən) is a documentation generator that works with many programming languages. It extracts information from specially-formatted source code comments and saves the information in one of various supported formats.
Doxygen supports static analysis of a codebase. It uses the parse tree parsed from the codebase to generate diagrams and charts of the code structure. It provides cross-referencing that a reader can use to refer back to the source code from the generated documentation.
Doxygen can be used in many programming contexts. It supports many languages including C, C++, C#, D, Fortran, IDL, Java, Objective-C, Perl, PHP, Python, and VHDL. It can run on many computers, including Unix-like, macOS, and Windows systems. It is free software, released under the terms of the GNU General Public License version 2 (GPLv2).

## History

The first version of Doxygen borrowed code from an early version of DOC++, developed by Roland Wunderling and Malte Zöckler at Zuse Institute Berlin. Later, the Doxygen code was rewritten by Dimitri van Heesch.

## Development

The Doxygen source code is hosted at GitHub, where the main developer, Dimitri van Heesch, contributes under the name "doxygen". Doxygen is written in C++, and consists of around 300,000 source lines of code. For lexical analysis, Lex (or its replacement Flex) is run via approximately 35,000 lines of lex script. The parsing tool Yacc (or its replacement Bison) is also used, but only for minor tasks. The bulk of parsing is done via native C++ code. The build system includes CMake and Python script.

## Design

Like other documentation generators such as Javadoc, Doxygen extracts information from both the comment and the symbolic (non-comment) code. A comment is associated with a programming symbol by immediately preceding it in the code. Markup in the comments allows for controlling inclusion and formatting of the resulting documentation.
Doxygen supports output in many formats including: HTML, CHM, RTF, PDF, LaTeX, PostScript and man page.
Doxygen can generate inheritance diagrams for C++ classes. For more advanced diagrams and graphs, Doxygen can use the "dot" tool from Graphviz.

## Example

All examples are given for languages with C-like comments where a multi-line comment starts with /* and a single line comment starts with //.
Doxygen ignores a comment unless it is marked specially. For a multi-line comment, the comment must start with /** or /*!. A markup tag is prefixed with a backslash (\) or an at-sign (@). The following is a relatively simple function comment block with markup in bold:
A block can be formatted various ways. A common way is to left-align asterisks on each line which Doxygen does not include in the output. For example:
Alternatively, a block can consist of a series of single-line comments. Doxygen accepts comments with an additional slash (/) or exclamation (!).
To locate a documentation comment to the right of the code, an additional < marker is required. This allows for an alternative approach for documenting parameters as shown below.
A mathematic formula can be specified via LaTeX commands. For example:
A more complete example in C++: