1 The data type of the interface

type name	C++	Python	DDS type
bool	bool	bool	boolean
byte	uint8_t	bytes	octet
char	char	str	char
float32	float	float	float
float64	double	float	double
int8	int8_t	int	octet
uint8	uint8_t	int	octet
int16	int16_t	int	short
uint16	uint16_t	int	unsigned short
int32	int32_t	int	long
uint32	uint32_t	int	unsigned long
int64	int64_t	int	long long
uint64	uint64_t	int	unsigned long long
string	std::string	str	string
wstring	std::u16string	str	wstring

1.1 Naming rules

1.Field names must be lowercase alphanumeric characters with underscores to separate words. 2.Field names must start with an alphabetic character, cannot end with an underscore, and can never have two consecutive underscores.

1.2 Set default values

uint8 x 42
int16 y -2000
string full_name "John Doe"
int32[] samples [-200, -100, 0, 100, 200]

1.3 Setting constants

int32 X=123
int32 Y=-123
string FOO="foo"
string EXAMPLE='bar'

2 Create an interface package

ros2 pkg create --build-type ament_cmake tutorial_interfaces

3 Create an interface directory

mkdir msg
mkdir srv
mkdir action

4 Define the interface

4.1 Num.msg file in the msg directory

int num

4.2 AddThreeInts.srv file in the srv directory

int64 a
int64 b
int64 c
---
int64 sum

4.3 The Fibonacci.action file in the action directory

int32 order
---
int32[] sequence
---
int32[] partial_sequence

5 CMakeLists.txt build

find_package(rosidl_default_generators REQUIRED)

rosidl_generate_interfaces(${PROJECT_NAME}
  "msg/Num.msg"
  "srv/AddThreeInts.srv"
  "action/Fibonacci.action"
)

6 package.xml add dependencies

<build_depend>rosidl_default_generators</build_depend>

<exec_depend>rosidl_default_runtime</exec_depend>

<depend>action_msgs</depend>

<member_of_group>rosidl_interface_packages</member_of_group>

7 Build the package

colcon build --packages-select tutorial_interfaces

6 Interface File