Coding Standard

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Revision as of 11:18, 30 August 2007 by Deepakgupta 011 (Talk | contribs)
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The increasing number of contributors require that we clearly define coding rules and guidelines. Although for historical reasons the current code of Stellarium does not always comply to these rules, they should now be respected for any addition or modification of the code.


Stylistic Conventions

File Names

The extensions are .hpp/.cpp for C++ headers/code, .h/.c for C headers/code. C++ files should have the same name and case than the class they contain. For example class StelFontMgr should be declared in file StelFontMgr.hpp and implemented in StelFontMgr.cpp.

Doxygen Comments

Stellarium source code should be documented with Doxygen. From Doxygen webpage:

"Doxygen is a documentation system for C++, C, Java, [...] 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. [...] The documentation is extracted directly from the sources, which makes it much easier to keep the documentation consistent with the source code. [...] You 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.

All public and protected classes and methods from Stellarium should be fully documented in the headers (.hpp).

There are different ways to comment C++ code with Doxygen, in Stellarium use the following for headers files:

//! Find and return the list of at most maxNbItem objects auto-completing the passed object I18n name.
//! @param objPrefix the case insensitive first letters of the searched object.
//! @param maxNbItem the maximum number of returned object names.
//! @return a vector of matching object name by order of relevance, or an empty vector if nothing match.
vector<wstring> listMatchingObjectsI18n(const wstring& objPrefix, unsigned int maxNbItem=5) const;

Brief descriptions are single line only, and stop at the first full stop (period). Any subsequent sentences which occur before @param or a similar tag are considered to be part of a detailed description.

For methods definitions in .cpp files, a simpler comment for each method is sufficient:

 Find and return the list of at most maxNbItem objects auto-completing the 
 passed object I18n name.
vector<wstring> listMatchingObjectsI18n(const wstring& objPrefix, unsigned int maxNbItem=5) const

C/C++ code

Use C++ replacement for C functions wherever possible. This includes the following:

  • Use std::string instead of char*
  • Use iostream C++ classes instead of C file managment with fopen().
  • Pass objects as references when needed instead of using pointers.
  • Include standard headers the C++ way, it is more portable:
#include <stdio.h> // Bad
#include <cstdio>  // Good
  • Avoid using pointers when not needed, this prevents creating memory leaks. For example:
string mapFileName = getDataDir() + "fontmap.dat";
ifstream *mapFile = new ifstream(mapFileName.c_str());  // Bad 
ifstream mapFile(mapFileName.c_str());                              // Good
  • Use STL containers such as std::vector or std::map, they are extremely efficient. Documentation is here.
  • Avoid using global function and variable. Encapsulate them in classes or namespaces as static members/variable.
  • Avoid using C macro, use static const variables instead. It is safer because it is type safe.
#define RADIUS 12 // Bad 
static const int RADIUS = 12;
  • Use stdc++ math functions instead of C ones. There are more protable and are also overrided for float, thus may be faster.
double cosLat = cos(lat);     // Bad 
double cosLat = std::cos(lat); // Good

Translatable strings and text console output

In Stellarium, translatable text is translated using the Translator class, which is a C++ wrapper to gettext. The translation process is done using the _() macro which takes in input a std::string in english and return in output a std::wstring (a string of wide characters) translated in another language using the current global language.

  • Translatable text in sources or in data files should be written in English, encoded in ASCII or UTF-8 if needed.
  • Translatable text should obey English typo conventions, for example there should be no space before ':'
wstring myTranslatedText = _("Distance of the planet :") // Bad
wstring myTranslatedText = _("Distance of the planet:")  // Good
  • When modifying the code, avoid to modify translatable string unless really needed. Any modification on one of them means that all the translators for all the langages will have to re-translate the new string.
  • In general no translated text (i.e. no wstring) should be output on the console because there are problems when string and wstring are output on the same console. This means that you should never use wcout, wcerr or wprintf(). Console output should be used for informations, errors and warnings which are not required by the user in nominal use.
  • Errors and warnings should be output in the stderr file, not stdout.
cout << "Error while opening file " << myFileName << "." << endl; // Bad 
cerr << "Error while opening file " << myFileName << "." << endl; // Good

Automated code formatting

You can use the astyle program to format your code according to these conventions. Use the following options:

astyle --style=ansi -tU source.cpp

Note that this command will replace the file source.cpp with the re-formatted one, and create a backup of the original with the .orig suffix. Also note that the -U option (used to un-pad parenthesis) is only available recent version of astyle.

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