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Doxygen Internals {#mainpage}


This page provides a high-level overview of the internals of doxygen, with links to the relevant parts of the code. This document is intended for developers who want to work on doxygen. Users of doxygen are referred to the User Manual.

The generic starting point of the application is of cource the main() function.

Configuration options

Configuration file data is stored in singleton class Config and can be accessed using wrapper macros Config_getString(), Config_getInt(), Config_getList(), Config_getEnum(), and Config_getBool() depending on the type of the option.

The format of the configuration file (options and types) is defined by the file config.xml. As part of the build process, the python script configgen.py will create a file configoptions.cpp from this, which serves as the input for the configuration file parser that is invoked using Config::parse(). The script configgen.py will also create the documentation for the configuration items, creating the file config.doc.

Gathering Input files

After the configuration is known, the input files are searched using searchInputFiles() and any tag files are read using readTagFile()

Parsing Input files

The function parseFiles() takes care of parsing all files. It uses the ParserManager singleton factory to create a suitable parser object for each file. Each parser implements the abstract interface ParserInterface.

If the parser indicates it needs preprocessing via ParserInterface::needsPreprocessing(), doxygen will call preprocessFile() on the file.

A second step is to convert multiline C++-style comments into C style comments for easier processing later on. As side effect of this step also aliases (ALIASES option) are resolved. The function that performs these 2 tasks is called convertCppComments().

Note: Alias resolution should better be done in a separate step as it is now coupled to C/C++ code and does not work automatically for other languages!

The third step is the actual language parsing and is done by calling ParserInterface::parseInput() on the parser interface returned by the ParserManager.

The result of parsing is a tree of Entry objects. These Entry objects are wrapped in a EntryNav object and stored on disk using Entry::createNavigationIndex() on the root node of the tree.

Each Entry object roughly contains the raw data for a symbol and is later converted into a Definition object.

When a parser finds a special comment block in the input, it will do a first pass parsing via parseCommentBlock(). During this pass the comment block is split into multiple parts if needed. Some data that is later needed is extracted like section labels, xref items, and formulas. Also Markdown markup is processed using processMarkdown() during this pass.

Resolving relations

The Entry objects created and filled during parsing are stored on disk (to keep memory needs low). The name, parent/child relation, and location on disk of each Entry is stored as a tree of EntryNav nodes, which is kept in memory.

Doxygen does a number of tree walks over the EntryNav nodes in the tree to build up the data structures needed to produce the output.

The resulting data structures are all children of the generic base class called Definition which holds all non-specific data for a symbol definition.

Definition is an abstract base class. Concrete subclasses are - ClassDef: for storing class/struct/union related data - NamespaceDef: for storing namespace related data - FileDef: for storing file related data - DirDef: for storing directory related data

For doxygen specific concepts the following subclasses are available - GroupDef: for storing grouping related data - PageDef: for storing page related data

Finally the data for members of classes, namespaces, and files is stored in the subclass MemberDef.

Producing debug output

Within doxygen there are a number of ways to obtain debug output. Besides the invasive method of putting print statements in the code there are a number of easy ways to get debug information.

  • Compilation of .l files
    This is also an invasive method but it will be automatically done by the flex / lex command. The result is that of each input line the (lex) rule(s) that are applied on it are shown.
  • windows
    • in the Visual C++ GUI
    • find the required .l file
    • select the Properties of this file
    • set the item Write used lex rules to Yes
    • see to it that the .l file is newer than the corresponding .cpp file or remove the corresponding .cpp file
  • unices
    • global change
      In the chapter "Doxygen's internals" a perl script is given to toggle the possibility of having the rules debug information.
    • command line change
      It is possible to the option LEX="flex -d" with the make command on the command line. In this case the .l that are converted to the corresponding .cpp files during this make get the rules debug information.
      To undo the rules debug information output just recompile the file with just make.
      Note this method applies for all the .l files that are rebuild to .cpp files so be sure that only the .l files(s) of which you want to have the rules debug information is (are) newer than the corresponding .cpp file(s).
  • Running doxygen
    During a run of doxygen it is possible to specify the -d option with the following possibilities (each option has to be preceded by -d):
  • findmembers
    Gives of global, class, module members its scope, arguments and other relevant information.
  • functions
    Gives of functions its scope, arguments and other relevant information.
  • variables
    Gives of variables its scope and other relevant information.
  • classes
    Gives of classes en modules its scope and other relevant information.
  • preprocessor
    Shows the results of the preprocessing phase, i.e. results from include files, <tt>#define</tt> statements etc., definitions in the doxygen configuration file like: EXPAND_ONLY_PREDEF, PREDEFINED and MACRO_EXPANSION.
  • commentcnv
    Shows the results of the comment conversion, the comment conversion does the following:
    • It converts multi-line C++ style comment blocks (that are aligned) to C style comment blocks (if MULTILINE_CPP_IS_BRIEF is set to NO).
    • It replaces aliases with their definition (see ALIASES)
    • It handles conditional sections (<tt>\cond ... \endcond</tt> blocks)
  • commentscan
    Will print each comment block before and after the comment is interpreted by the comment scanner.
  • printtree
    Give the results in in pretty print way, i.e. in an XML like way with each level indented by a "." (dot).
  • time
    Provides information of the different stages of the doxygen process.
  • extcmd
    Shows which external commands are executed and which pipes are opened.
  • markdown
    Will print each comment block before and after Markdown processing.
  • filteroutput
    Gives the output of the output as result of the filter command (when a filter command is specified)
  • validate
    Currently not used
  • lex
    Provide output of the lex files used. When a lexer is started and when a lexer ends the name of the lex file is given so it is possible to see in which lexer the problem occurs. This makes it easier to select the file to be compiled in lex debug mode.

Producing output


Topics TODO

  • Grouping of files in Model / Parser / Generator categories
  • Index files based on IndexIntf
  • HTML navigation
  • HTML Help (chm)
  • Documentation Sets (XCode)
  • Qt Help (qhp)
  • Eclipse Help
  • Search index
  • Javascript based
  • Server based
  • External
  • Citations
  • via bibtex
  • Various processing steps for a comment block
  • comment conversion
  • comment scanner
  • markdown processor
  • doc tokenizer
  • doc parser
  • doc visitors
  • Diagrams and Images
  • builtin
  • via Graphviz dot
  • via mscgen
  • PNG generation
  • Output formats: OutputGen, OutputList, and DocVisitor
  • Html: HtmlGenerator and HtmlDocVisitor
  • Latex: LatexGenerator and LatexDocVisitor
  • RTF: RTFGenerator and RTFDocVisitor
  • Man: ManGenerator and ManDocVisitor
  • XML: generateXML() and XmlDocVisitor
  • print: debugging via PrintDocVisitor
  • text: TextDocVisitor for tooltips
  • perlmod
  • i18n via Translator and language.cpp
  • Customizing the layout via LayoutDocManager
  • Parsers
  • C Preprocessing
    • const expression evaluation
  • C link languages
  • Python
  • Fortran
  • VHDL
  • TCL
  • Tag files
  • Marshaling to/from disk
  • Portability functions
  • Utility functions