ros packages with C++14 lambda support - c++

Question

Ok, since I'm working on a private project using ROS Framework, my motivation was raised by the new C++14 auto lambda feature (see this link for a better explanation).
the problem I am facing is that ROS framework is sticking to the old days C++03 for it's compilation. So, how can I enable C++14 compilation support and how can I use the lambda functions ?
Here's a simple nodes for testing with the lambda function (in the subscriber node) :
publisher :
#include <ros/ros.h>
#include <std_msgs/String.h>
#include <std_msgs/Int8.h>
#include <sstream>
int main(int argc, char **argv)
{
ros::init(argc, argv, "talker");
ros::NodeHandle n;
ros::Publisher string_pub = n.advertise<std_msgs::String>("chatter_string", 1000);
ros::Publisher int_pub = n.advertise<std_msgs::Int8>("chatter_int", 1000);
ros::Rate loop_rate(10);
int count = 0;
while (ros::ok())
{
std_msgs::String str_msg;
std::stringstream ss;
ss << "hello world ";
str_msg.data = ss.str();
std_msgs::Int8 int_msg;
int_msg.data = count;
string_pub.publish(str_msg);
int_pub.publish(int_msg);
ros::spinOnce();
loop_rate.sleep();
++count;
}
return 0;
}
subscriber :
#include <ros/ros.h>
#include <std_msgs/String.h>
#include <std_msgs/Int8.h>
//generic lambda to add two variables
auto func = [](auto input) { return input + input; };
void StringCallback(const std_msgs::String::ConstPtr& msg)
{
ROS_INFO("I heard: [%s]", func(msg->data).c_str());
}
void IntCallback(const std_msgs::Int8::ConstPtr& msg)
{
int result = msg->data;
ROS_INFO("I heard: [%d]", func(result));
}
int main(int argc, char **argv)
{
ros::init(argc, argv, "listener");
ros::NodeHandle n;
ros::Subscriber string_sub = n.subscribe("chatter_string", 1000, StringCallback);
ros::Subscriber int_sub = n.subscribe("chatter_int", 1000, IntCallback);
ros::spin();
return 0;
}
CMakeLists :
cmake_minimum_required(VERSION 2.8.3)
project(tutocpp14)
find_package(catkin REQUIRED COMPONENTS
roscpp
rospy
std_msgs
)
catkin_package()
include_directories( ${catkin_INCLUDE_DIRS} include )
add_executable(listener src/listener.cpp)
add_executable(publisher src/publisher.cpp)
target_link_libraries(listener ${catkin_LIBRARIES})
target_link_libraries(publisher ${catkin_LIBRARIES})
Making the package after this configuration throw me the following error :
tutocpp14/src/listener.cpp:10:43: error: ‘func’ was not declared in this scope
ROS_INFO("I heard: [%s]", func(msg->data).c_str());

Answer 1

It turned out that I can add the C++14 to ROS for my package compilation. Although this is not advised for publishing the packages.
Use of C++11/C++14 features and filesystem/networking/etc... TS's (Technical Specifications) is allowed if they are checked for at configure time and equivalent functionality can be provided with the extra compiler features. Support for C++11 is now a compiler requirement, but the API of the packages included in desktop-full will not use any C++11-specific feature. External packages are encouraged to follow this guideline.
But, still that I am not intending to publish my work for now, so, I can get myself the permit to do so.
To get C++14 support for a ROS package, I have to set the -std=c++14 flag by adding the following lines in my CMakelists.txt file :
# check c++14 / c++0x
include(CheckCXXCompilerFlag)
CHECK_CXX_COMPILER_FLAG("-std=c++14" COMPILER_SUPPORTS_CXX14)
CHECK_CXX_COMPILER_FLAG("-std=c++0x" COMPILER_SUPPORTS_CXX0X)
if(COMPILER_SUPPORTS_CXX14)
set(CMAKE_CXX_FLAGS "-std=c++14")
elseif(COMPILER_SUPPORTS_CXX0X)
set(CMAKE_CXX_FLAGS "-std=c++0x")
else()
message(FATAL_ERROR "The compiler ${CMAKE_CXX_COMPILER} has no C++14 support. Please use a different C++ compiler.")
endif()
this will check the existence of C++14 in the compiler and throw an error if not. Now, it works like a charm.
Hope that helps. Cheers.