ROS Resources: Documentation | Support | Discussion Forum | Index | Service Status | ros @ Robotics Stack Exchange
Ask Your Question

How to get an array of parameters with rclcpp

asked 2018-06-27 16:32:15 -0500

David Lu gravatar image

In ROS1, you could retrieve a list of parameters

The documentation shows get_parameter returning an ParameterVariant but ParameterVariant doesn't seem to have an as_vector option.

edit retag flag offensive close merge delete


Do you want a list of parameters in a certain namespace, like /ns/* -> ['value of /ns/foo', 'value of /ns/bar', 'value of /ns/baz'], or do you want one parameter as a vector (e.g. parameter /position -> [1.0, 1.0, 0.0])?

William gravatar image William  ( 2018-06-27 17:18:30 -0500 )edit

The latter, one parameter name, which is why I figured get_parameters wouldn't work.

David Lu gravatar image David Lu  ( 2018-06-27 17:51:05 -0500 )edit

We may not have that API yet, but we can certainly add it or whatever the appropriate alternative is. There was some work done on lists in parameters this cycle, but I don't know the state off-hand, let me look it up.

William gravatar image William  ( 2018-06-27 17:59:12 -0500 )edit

4 Answers

Sort by ยป oldest newest most voted

answered 2018-06-27 18:08:33 -0500

William gravatar image

For the slightly different case than what @tfoote linked to, here's how to get a single parameter as an array of values.

We recently merged this feature (made by @ayrton04), see:

Looks like there's no documentation yet, but there is an example of setting:

And you can use get_parameter(s) to get the rclcpp::Parameter for it, and on that class there are as_*_array() methods:

Which return vector<T>.

edit flag offensive delete link more


Is there a way to achieve this by just using this->declare_parameter<float>("foo", 15.0); this->get_parameter("foo", foo); syntax? Or in this example how come that the parameter doesn't need to be declared? From reading a long issue involving some 2 booleans with undeclared_auto_param_something_something and another boolean I just got that you always should declare your params, but this example doesn't do that? And is the documentation 2years later still missing?

Hakaishin gravatar image Hakaishin  ( 2020-12-02 03:41:07 -0500 )edit

answered 2018-06-27 16:59:23 -0500

tfoote gravatar image

updated 2018-06-27 18:07:52 -0500

There's get_parameters() one line above which takes a vector of names and returns a vector of ParameterVariants


Sorry I thought you wanted to list multiple parameters. We also support arrays of primatives. It looks like the documentation is not complete.

The ParameterVarient includes ARRAY types natively

The get_value method on the variant will return the vector value. We don't have it in the demos but there are tests covering it you can use as an example, here

edit flag offensive delete link more

answered 2020-12-02 03:59:14 -0500

Hakaishin gravatar image

Inspired by williams answer and checking out the newest commit on master here: I found below code to work, not sure if this is the recommended way, but it works.

rclcpp::Parameter foo_param("foo", std::vector<double>({}));
this->get_parameter("foo", foo_param);
std::vector<double> foo = foo_param.as_double_array();
edit flag offensive delete link more

answered 2022-04-16 17:28:16 -0500

clyde gravatar image

The syntax has been getting easier over time. Here is a simple way to declare and get a vector of integers in Galactic:

auto foo = declare_parameter<std::vector<int64_t>>("param", std::vector<int64_t>({1, 2, 3}));
edit flag offensive delete link more


This shows how to declare the parameter. But how would you get a param holding a vector using the 'get_parameter' syntax?

swiz23 gravatar image swiz23  ( 2022-11-23 11:23:16 -0500 )edit

declare_parameter also gets the parameter. But if you need to use get_parameter, it looks like that isn't possible right now.

clyde gravatar image clyde  ( 2022-11-23 12:54:43 -0500 )edit

Ah, so when you do 'auto foo', is 'foo' of the std::vector<int64_t> type? Or is 'foo' of the rclcpp::Parameter type? Also, besides for declaring the parameter, you're saying that it also tries to get the parameter, and if it can't find it, it will default it to std::vector<int64_t>({1, 2, 3})?

swiz23 gravatar image swiz23  ( 2022-11-23 13:35:07 -0500 )edit

foo is std::vector<int64_t>. Yes, that is the default.

clyde gravatar image clyde  ( 2022-11-23 13:53:02 -0500 )edit

I did not know that! Thanks!

swiz23 gravatar image swiz23  ( 2022-11-23 14:08:25 -0500 )edit

Question Tools



Asked: 2018-06-27 16:32:15 -0500

Seen: 5,135 times

Last updated: Apr 16 '22