# C++ coding style guide¶

## 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¶

### Indentation¶

Indentation should be two spaces and it should be spaces. Do not use tab(s).

Comment your code, and do it often. Capitalize the first letter and don’t use punctuation (unless the comment runs over several sentences). Here’s a good example from TopologyComputation.cpp:

// Check if connectivity has already been computed
if (connectivity.size() > 0)
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.size() > 0)
return;

...


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

### Integers and reals¶

Use std::size_t instead of int (unless you really want to use negative integers or memory usage is critical).

std::size_t i = 0;
double x = 0.0;


### Placement of brackets and indent style¶

Use the BSD/Allman style when formatting blocks of code, i.e., curly brackets following multiline control statements should appear on the next line and should not be indented:

for (std::size_t i = 0; i < 10; i++)
{
...
}


For one line statements, omit the brackets:

for (std::size_t i = 0; i < 10; i++)
foo(i);


// Copyright (C) 2008 Foo Bar
//
// This file is part of DOLFIN.
//
// DOLFIN is free software: you can redistribute it and/or modify
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// DOLFIN is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with DOLFIN. If not, see <http://www.gnu.org/licenses/>.
//
// Modified by Bar Foo 2008

#ifndef __FOO_H
#define __FOO_H

namespace dolfin
{

class Bar; // Forward declarations here

/// Documentation of class

class Foo
{
public:

...

private:

...

};

}

#endif


### Implementation file layout¶

Implementation files should follow the below template:

// Copyright (C) 2008 Foo Bar
//
// This file is part of DOLFIN.
//
// DOLFIN is free software: you can redistribute it and/or modify
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// DOLFIN is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public License
// along with DOLFIN. If not, see <http://www.gnu.org/licenses/>.
//
// Modified by Bar Foo 2008

#include <dolfin/Foo.h>

using namespace dolfin;

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


The horizontal lines above (including the slashes) should be exactly 79 characters wide.

### Including header files and using forward declarations¶

Do not use #include <dolfin.h> or #include <dolfin/dolfin_foo.h> inside the DOLFIN source tree. Only include the portions of DOLFIN 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[]).

### Prefer smart pointers over plain pointers¶

Use std::shared_ptr and std::unique_ptr in favour of plain pointers. Smart pointers reduce the likelihood of memory leaks and make ownership clear. Use unique_ptr for a pointer that is not shared and shared_ptr when multiple pointers point to the same object.