CODINGSTYLE.md

SuperTux Coding Standards

Language

C++17 is the main langauge used for this project. GCC, Clang and MSVC are supported.

For better backward compatibilty with older compiler, namely gcc5, some C++17 features are restricted:

• generic lambda functions are not allowed, e.g. [](auto foo){}
• tuple constructors have to be explicit, e.g. std::tuple<int, int>{5, 6}, not {5, 6}

Repository Structure

Properly separate between generic engine code and game specific code whenever feasible.

Third party libraries are not allowed in src/, they go to external/.

Third party libraries that are imported into external/ as git submodule have to be forked and included into the SuperTux organisation on Github, not directly included from upstream.

File Formating

Do not have spaces at the end of lines.

Files should always end with /* EOF */ and a newline or a similar marker approprimate for the given language. This marker can be left out for fileformats that have an end tag, e.g. </html>.

Aim for one file per class, small helper classes in the same file are ok.

Includes

The path in #include directives must not contain ...

All paths for includes from SuperTux must be relative to the src/ directory and use #include "...".

Use the #include <> syntax for libraries in external/, use cmake to set the include path properly.

The order of includes shall be as follows, each of those subgroups shall be ordered alphabetically:

• include of header file when in a .cpp file
• include of the base class in a header file of a derived class
• system includes
• external includes
• local includes

Conditional includes should be indented.

#ifdef FOOBAR
#  include "foobar.hpp"
#endif

Include guards are of the form:

#ifndef HEADER_SUPERTUX_{PATH}_{FILE}_HPP
#define HEADER_SUPERTUX_{PATH}_{FILE}_HPP

tools/fix_include_guards.sh is a little script that will help to fix include guards on file renames.

Variables

Prefix member variable names with m_, global variables with g_, and static variables with s_. DynamicScopeRefs are prefixed with d_.

Classes

Mark all classes as final unless they are specifically designed with polymorphism in mind.

Mark all functions that override a virtual function in a base class with override.

Write simple getters/setters inside a header file on a single line. Mark them as inline.

Properly separate data members and member functions. Do not mix them in the same public/protected/private section.

List virtual functions before non-virtual functions.

The order of declarations in a class shall be as follows:

class Foo final
{
public:
protected:
private:
   // type declarations, needs to come first as later stuff might depend on them

public:
protected:
private:
   // static stuff

public:
protected:
private:
   // constructors
   // destructor

public:
protected:
private:
   // virtual member functions
   // non-virtual member functions

public:
protected:
private:
   // member variables with an m_ prefix

private:
  // non-copyable footer
  Foo(const Foo&) = delete;
  Foo& operator=(const Foo&) = delete;
};

Pointers

Do not use raw pointers and new/delete, use std::unique_ptr<>/std::make_unique<> instead.

Only use std::smart_ptr<> when sharing of data is required, prefer std::unique_ptr<> when possible.

Pass and return values as value, & or const&, only use * when the value is expected to be nullptr.

Do not pass values as const std::unique_ptr<T>& or const std::shared_ptr<T>&, dereference the pointer and pass as const&.

To check for nullptr, use an if statements with initializer when possible:

if (auto* ptr = get_ptr()) {
  // code here
}

auto

Don't use auto for basic types (int, float, std::string, ...)

Only use auto when the exact type is unnecessary to know (e.g. iterators) or obvious from the context, (e.g. auto foo = Foo::create())

Capture pointers as auto*, not just auto.

Use const auto& for loops to avoid copies.

Namespaces

Namespaces should be written in the form:

namespace my_namespace {
...
} // namespace my_namespace

With no newline before the {. Do not indent the content inside the namespace. The namespace itself should be all lowercase.

Compiler Warnings and Errors

Compile with a maximum warning level and with -Werror. This can be accomplished with:

cmake .. -DCMAKE_BUILD_TYPE=Release  -DWARNINGS=ON -DWERROR=ON

This requires, among other things:

• use of final and override keywords

• use of static_cast and reinterpret_cast, not old style C casts

• all member variables have to be initialized in the constructor

• all int/float conversion has to be explicit

Comments

Avoid comments unless they explain something important and non-obvious. Document why the code does something, not what it does.

Prefer to use good function and variable names to create self-documenting code.

Use the // syntax for regular comments, even multiline, don't use /* */.

For Doxygen (code documentation), use the /** */ syntax, don't use /**< and other styles of comments.

For translator information, use the // l10n: syntax.

Don't do * prefix decorations in comments, keep things simple and compact:

/*
 *  Don't do this
 */

Instead:

// Do this

or:

/** Also ok when it's a Doxygen comment */

Spaces

Use a space after if/while/switch/for:

for (int i = 0; i < len; ++i) ...

if (a > b) ...

while (a > b) ...

switch (myenum) ...

But don't use a space after a function name:

myfunc () // don't do this

myfunc() // do this

Line breaks

Write simple getters/setters inside a header file on a single line:

Vector get_pos() const { return m_pos; }

Don't include more complex functions inside a header file, unless it's necessary (template, performance).

Declare functions like:

ReturnType
ClassName::function_name()
{
...
}

We don't have any hard rules on linebreaks before { inside functions, but generally prefer the no-linebreak version when doing simple one-liners and the other one when doing more complex stuff:

if (foo) {
  one_line_function_call()
}

if (foo)
{
  long();
  complex();
  series();
  of();
  calls();
}

Other Information

More general info on good practices can be found in Google's C++ Style Guide and in the C++ Core Guidelines, note however that we do not strictly follow either of them and divert from them in some points, so just take them as general guidelines, not hard rules.