Software Coding Standards

File Layout

• Header files should have a ".h" extension

• Header files always go either into "include" or a sub-directory of "include"

• C++ source files should have a ".C" extension

• Source files go into "src" or a subdirectory of "src".

Files

Header and source file names must match the name of the class that the files define. Hence, each set of .h and .C files should contain code for a single class. Helper classes or classes not exposed to the user are an exception to this rule.

• src/ClassName.C

• include/ClassName.h

Naming

• ClassName Class names utilize camel case, note the .h and .C filenames must match the class name.

• methodName() Method and function names utilize camel case with the leading letter lower case.

• _member_variable Member variables begin with underscore and are all lower case and use underscore between words.

• local_variable Local variables are lowercase, begin with a letter, and use underscore between words

Use of C++ auto keyword

Use auto unless it complicates readability, but do not use it in a function or method declaration. Make sure your variables have good names when using auto!

  auto dof = elem->dof_number(0, 0, 0);
  auto & obj = getSomeObject();
  auto & elem_it = mesh.active_local_elements_begin();
  auto & item_pair = map.find(some_item);

  // Cannot use reference here
  for (auto it = obj.begin(); it != obj.end(); ++it)
    doSomething();

  // Use reference here
  for (auto & obj : container)
    doSomething();

Index Variables in Looping Constructs

In keeping with good auto practices, it would be really nice if we could use auto for loop indices in places where range loops aren't convenient or possible. Unfortunately, the most natural code one would like to write yields a warning with our default compiler flags:

  for (auto i = 0; i < v.size(); ++i) // DON'T DO THIS!

  warning: comparison of integers of different signs: 'int' and 'std::__1::vector<int, std::__1::allocator<int> >::size_type' (aka 'unsigned long')

The ideal solution would be to match the type you are looping over, but this is slightly more difficult than just using decltype due to qualifiers like const. In MOOSE we have solved this for you with MooseIndex:

  // Looping to a scalar index
  for (MooseIndex(n_nodes) i = 0; i < nodes; ++i)
    ... Do something with index i

  // Looping to a container size (where range-for isn't sufficient)
  for (MooseIndex(vector) i = 0; i < vector.size(); ++i)
    ... Do something with index i

Lambdas

List captured variables (by value or reference) in the capture list explicitly where possible.

  std::for_each(container.begin(), container.end(), [=local_var](Foo & foo) {
    foo.item = local_var;
  });

Other C++ Notes

• Use the override keyword on overridden virtual methods

• Use std::make_shared<T>() when allocating new memory for shared pointers

• Use std::make_unique<T>() when allocating new memory for unique pointers

• Make use of std::move() for efficiency when possible

Variable Initialization

When creating a new variable use these patterns:

unsigned int i = 4;  // Built-in types
SomeObject junk(17); // Objects
SomeObject * stuff = new SomeObject(18); // Pointers

Trailing Whitespace and Tabs

Tabs and trailing whitespace are not allowed in the C++ in the repository. Running the following one-liner from the root directory of your repository will format the code correctly.

find . -name '*.[Chi]' -or -name '*.py' | xargs perl -pli -e 's/\s+$//'

C++ Includes

Only include things that are absolutely necessary in header files. Please use forward declarations when possible.

// Forward declarations
class Something;

All non-system includes should use quotes with a single space between include and the filename.

#include "LocalInclude.h"
#include "libmesh/libmesh_include.h"

#include <system_library>

Documentation

• In source documentation should be extensive, designed toward the software developer, and be formatted for the use of Doxygen.

Python

Where possible, follow the above rules for Python. The only modifications are:

1. Four spaces are used for indenting and

2. Member variables should be named as follows:

class MyClass:
    def __init__(self):
        self.public_member
        self._protected_member
        self.__private_member

Code Commandments

• Use references instead of pointers whenever possible. - i.e., this object lives for a shorter period of time than the object it needs to refer to does

• Methods should return pointers to objects if returned objects are stored as pointers and references if returned objects are stored as references.

• When creating a new class: - Include dependent header files in the *.C file whenever possible (i.e. the header uses only references or pointers in it's various declarations) and use forward declarations in the header file as needed. - One exception is when doing so would require end users to include multiple files to complete definitions of child objects (Errors typically show up as "incomplete class" or something similar during compilation).

• Avoid using a global variable when possible.

• Every destructor must be virtual.

• All function definitions should be in *.C files. - The only exceptions are for inline functions for speed and templates.

• Thou shalt not commit accidental insertion in a std::map by using brackets in a right-hand side operator unless proof is provided that it can't fail.

• Thou shalt use range-based loops or MooseIndex() based loops for iteration.