C++

Warning

Under Construction

References

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

1. https://docs.ros.org/en/humble/Contributing/Code-Style-Language-Versions.html
2. https://www.autosar.org/fileadmin/standards/adaptive/22-11/AUTOSAR_RS_CPP14Guidelines.pdf
3. https://isocpp.github.io/CppCoreGuidelines/CppCoreGuidelines

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

```cpp // Compliant

include "my_header.hpp"

include "my_package/foo.hpp"

include

include

include

include

include

```

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

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

```cpp // Non-compliant

include

include

define EIGEN_MPL2_ONLY

include "my_header.hpp"

include "my_package/foo.hpp"

include

include

include

include

```

Instead, define macros before #include lines.

```cpp // Compliant

define EIGEN_MPL2_ONLY

include "my_header.hpp"

include "my_package/foo.hpp"

include

include

include

include

include

include

```

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

```cpp // Compliant

include "my_header.hpp"

include "my_package/foo.hpp"

include

include

include

include

include

// For the foo bar reason, the FOO_MACRO must be defined here.

define FOO_MACRO

include

```

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

cpp 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

cpp 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

cpp 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

cpp class RosApi; RosApi ros_api;