C++ style guide

Formatting

clang-format is used to format files. A .clang-format file is included in the root directory. Editors can be configured to apply the style using clang-format.

Naming conventions

Class names

Use camel caps for class names:

class FooBar
{
  ...
};

Function names

Use lower-case for function names and underscore to separate words:

foo();
bar();
foo_bar(...);

Functions returning a value should be given the name of that value, for example:

class Array:
{
public:

  /// Return size of array (number of entries)
  std::size_t size() const;

};

In the above example, the function should be named size rather than get_size. On the other hand, a function not returning a value but rather taking a variable (by reference) and assigning a value to it, should use the get_foo naming scheme, for example:

class Parameters:
{
public:

  /// Retrieve all parameter keys
  void get_parameter_keys(std::vector<std::string>& parameter_keys) const;

};

Variable names

Use lower-case for variable names and underscore to separate words:

Foo foo;
Bar bar;
FooBar foo_bar;

Enum variables and constants

Enum variables should be lower-case with underscore to separate words:

enum Type {foo, bar, foo_bar};

We try to avoid using #define to define constants, but when necessary constants should be capitalized:

#define FOO 3.14159265358979

File names

Use camel caps for file names if they contain the declaration/definition of a class. Header files should have the suffix .h and implementation files should have the suffix .cpp:

FooBar.h
FooBar.cpp

Use lower-case for file names that contain utilities/functions (not classes).

Miscellaneous

Comments

Capitalize the first letter of a comment and don’t use punctuation (unless the comment runs over several sentences). Here’s an example:

// Check if connectivity has already been computed
if (!connectivity.empty())
  return;

// Invalidate ordering
mesh._ordered = false;

// Compute entities if they don't exist
if (topology.size(d0) == 0)
  compute_entities(mesh, d0);
if (topology.size(d1) == 0)
  compute_entities(mesh, d1);

// Check if connectivity still needs to be computed
if (!connectivity.empty())
  return;

...

Always use // for comments and /// for documentation. Never use /* foo */, not even for comments that runs over multiple lines.

Header file layout

Header files should follow the below template:

// Copyright (C) 2018 Foo Bar
//
// This file is part of DOLFINx (https://www.fenicsproject.org)
//
// SPDX-License-Identifier:    LGPL-3.0-or-later

#pragma once

namespace dolfinx
{

  class Bar; // Forward declarations here

  /// Documentation of class

  class Foo
  {
  public:

    ...

  private:

    ...

  };

}

Implementation file layout

Implementation files should follow the below template:

// Copyright (C) 2018 Foo Bar
//
// This file is part of DOLFINx (https://www.fenicsproject.org)
//
// SPDX-License-Identifier:    LGPL-3.0-or-later

#include <dolfinx/Foo.h>

using namespace dolfinx;

//-----------------------------------------------------------------------------
Foo::Foo() : // variable initialization here
{
  ...
}
//-----------------------------------------------------------------------------
Foo::~Foo()
{
  // Do nothing
}
//-----------------------------------------------------------------------------

Including header files and using forward declarations

Do not use #include <dolfinx.h> or #include <dolfinx/dolfin_foo.h> inside the DOLFINx source tree. Only include the portions of DOLFINx you are actually using.

Include as few header files as possible and use forward declarations whenever possible (in header files). Put the #include in the implementation file. This reduces compilation time and minimizes the risk of cyclic dependencies.

Explicit constructors

Make all one argument constructors (except copy constructors) explicit:

class Foo
{
  explicit Foo(std::size_t i);
};

Virtual functions

Always declare inherited virtual functions as virtual in the subclasses. This makes it easier to spot which functions are virtual.

class Foo
{
  virtual void foo();
  virtual void bar() = 0;
};

class Bar : public Foo
{
  virtual void foo();
  virtual void bar();
};

Use of libraries

Prefer C++ strings and streams over old C-style char*

Use std::string instead of const char* and use std::istream and std::ostream instead of FILE. Avoid printf, sprintf and other C functions.

There are some exceptions to this rule where we need to use old C-style function calls. One such exception is handling of command-line arguments (char* argv[]).

Avoid plain pointers

Use C++11 smart pointer and avoid plain pointers.