Doxygen是一种开源跨平台的，以类似JavaDoc风格描述的文档系统，完全支持C、C++、Java、Objective-C和IDL语言，部分支持PHP、C#。注释的语法与Qt-Doc、KDoc和JavaDoc兼容。Doxygen可以从一套归档源文件开始，生成HTML格式的在线类浏览器，或离线的LATEX、RTF参考手册。

Doxygen is the de facto standard tool for generating documentation from annotated C++ sources, but it also supports other popular programming languages such as C, Objective-C, C#, PHP, Java, Python, IDL (Corba, Microsoft, and UNO/OpenOffice flavors), Fortran, VHDL, Tcl, and to some extent D.

Doxygen can help you in three ways:

1)It can generate an on-line documentation browser (in HTML) and/or an off-line reference manual (in LaTeX) from a set of documented source files. There is also support for generating output in RTF (MS-Word), PostScript, hyperlinked PDF, compressed HTML, DocBook and Unix man pages. The documentation is extracted directly from the sources, which makes it much easier to keep the documentation consistent with the source code.

2)You can configure doxygen to extract the code structure from undocumented source files. This is very useful to quickly find your way in large source distributions. Doxygen can also visualize the relations between the various elements by means of include dependency graphs, inheritance diagrams, and collaboration diagrams, which are all generated automatically.

3)You can also use doxygen for creating normal documentation (as I did for the doxygen user manual and doxygen web-site).

Doxygen  Features

• Requires very little overhead from the writer of the documentation. Plain text will do, Markdown is support, and for more fancy or structured output HTML tags and/or some of doxygen's special commands can be used.
• Cross platform: works on Windows and many Unix flavors (including Linux and MacOSX).
• Indexes, organizes and generates browsable and cross-referenced output even from undocumented code.
• Generates structured XML output for parsed sources, which can be used by external tools.
• Supports C/C++, Java, (Corba and Microsoft) Java, Python, VHDL, PHP IDL, C#, Fortran, TCL, Objective-C 2.0, and to some extent D sources.
• Supports documentation of files, namespaces, packages, classes, structs, unions, templates, variables, functions, typedefs, enums and defines.
• JavaDoc (1.1), qdoc3 (partially), and ECMA-334 (C# spec.) compatible.
• Comes with a GUI frontend (Doxywizard) to ease editing the options and run doxygen. The GUI is available on Windows, Linux, and MacOSX.
• Automatically generates class and collaboration diagrams in HTML (as clickable image maps) and  (as Encapsulated PostScript images).
• Uses the dot tool of the Graphviz tool kit to generate include dependency graphs, collaboration diagrams, call graphs, directory structure graphs, and graphical class hierarchy graphs.
• Allows grouping of entities in modules and creating a hierarchy of modules.
• Flexible comment placement: Allows you to put documentation in the header file (before the declaration of an entity), source file (before the definition of an entity) or in a separate file.
• Generates a list of all members of a class (including any inherited members) along with their protection level.
• Outputs documentation in on-line format (XHTML and UNIX man page) and off-line format (  and RTF) simultaneously (any of these can be disabled if desired). All formats are optimized for ease of reading. 
  Furthermore, compressed HTML can be generated from HTML output using Microsoft's HTML Help Workshop (Windows only) and PDF can be generated from the  output.
• Support for various third party help formats including HTML Help, docsets, Qt-Help, and eclipse help.
• Includes a full C preprocessor to allow proper parsing of conditional code fragments and to allow expansion of all or part of macros definitions.
• Automatically detects public, protected and private sections, as well as the Qt specific signal and slots sections. Extraction of private class members is optional.
• Automatically generates references to documented classes, files, namespaces and members. Documentation of global functions, global variables, typedefs, defines and enumerations is also supported.
• References to base/super classes and inherited/overridden members are generated automatically.
• Includes a fast, rank based search engine to search for strings or words in the class and member documentation (PHP based).
• Includes an Javascript based live search feature to search for symbols as you type (for small to medium sized projects).
• You can type normal HTML tags in your documentation. Doxygen will convert them to their equivalent , RTF, and man-page counterparts automatically.
• Allows references to documentation generated for other (doxygen documented) projects (or another part of the same project) in a location independent way.
• Allows inclusion of source code examples that are automatically cross-referenced with the documentation.
• Inclusion of undocumented classes is also supported, allowing to quickly learn the structure and interfaces of a (large) piece of code without looking into the implementation details.
• Allows automatic cross-referencing of (documented) entities with their definition in the source code.
• All source code fragments are syntax highlighted for ease of reading.
• Allows inclusion of function/member/class definitions in the documentation.
• All options are read from an easy to edit and (optionally) annotated configuration file.
• Documentation and search engine can be transferred to another location or machine without regenerating the documentation.
• Supports many different character encodings and uses UTF-8 internally and for the generated output.
• Doxygen can generate a layout which you can use and edit to change the layout of each page.
• There more than a 100 configurable options to fine-tune the output.
• Can cope with large projects easily.