C++#

Warning

Under Construction

References#

Follow the guidelines below if a rule is not defined on this page.

Also, it is encouraged to apply Clang-Tidy to each file. For the usage, see Applying Clang-Tidy to ROS packages.

Note that not all rules are covered by Clang-Tidy.

Style rules#

Include header files in the defined order (required, partially automated)#

Rationale#

Due to indirect dependencies, the include system of C++ makes different behaviors if the header order is different.
To reduce unintended bugs, local header files should come first.

Reference#

https://llvm.org/docs/CodingStandards.html#include-style

Example#

Include the headers in the following order:

Main module header
Local package headers
Other package headers
Message headers
Boost headers
C system headers
C++ system headers

// Compliant
#include "my_header.hpp"

#include "my_package/foo.hpp"

#include <package1/foo.hpp>
#include <package2/bar.hpp>

#include <std_msgs/msg/header.hpp>

#include <iostream>
#include <vector>

If you use "" and <> properly, ClangFormat in pre-commit sorts headers automatically.

Do not define macros between #include lines because it prevents automatic sorting.

// Non-compliant
#include <package1/foo.hpp>
#include <package2/bar.hpp>

#define EIGEN_MPL2_ONLY
#include "my_header.hpp"
#include "my_package/foo.hpp"

#include <Eigen/Core>

#include <std_msgs/msg/header.hpp>

#include <iostream>
#include <vector>

Instead, define macros before #include lines.

// Compliant
#define EIGEN_MPL2_ONLY

#include "my_header.hpp"

#include "my_package/foo.hpp"

#include <Eigen/Core>
#include <package1/foo.hpp>
#include <package2/bar.hpp>

#include <std_msgs/msg/header.hpp>

#include <iostream>
#include <vector>

If there are any reasons for defining macros at a specific position, write a comment before the macro.

// Compliant
#include "my_header.hpp"

#include "my_package/foo.hpp"

#include <package1/foo.hpp>
#include <package2/bar.hpp>

#include <std_msgs/msg/header.hpp>

#include <iostream>
#include <vector>

// For the foo bar reason, the FOO_MACRO must be defined here.
#define FOO_MACRO
#include <foo/bar.hpp>

Use lower snake case for function names (required, partially automated)#

Rationale#

It is consistent with the C++ standard library.
It is consistent with other programming languages such as Python and Rust.

Exception#

For member functions of classes inherited from external project classes such as Qt, follow that naming convention.

Reference#

https://docs.ros.org/en/humble/The-ROS2-Project/Contributing/Code-Style-Language-Versions.html#function-and-method-naming

Example#

void function_name()
{
}

Use upper camel case for enum names (required, partially automated)#

Rationale#

It is consistent with ROS 2 core packages.

Exception#

Enums defined in the rosidl file can use other naming conventions.

Reference#

http://wiki.ros.org/CppStyleGuide (Refer to "15. Enumerations")

Example#

enum class Color
{
  Red, Green, Blue
}

Use lower snake case for constant names (required, partially automated)#

Rationale#

It is consistent with ROS 2 core packages.
It is consistent with std::numbers.

Exception#

Constants defined in the rosidl file can use other naming conventions.

Reference#

https://en.cppreference.com/w/cpp/numeric/constants

Example#

constexpr double gravity = 9.80665;

Count acronyms and contractions of compound words as one word (required, partially automated)#

Rationale#

To clarify the boundaries of words when acronyms are consecutive.

Reference#

https://rust-lang.github.io/api-guidelines/naming.html#casing-conforms-to-rfc-430-c-case

Example#

class RosApi;
RosApi ros_api;