How to read a vector<strings> parameter from command line

Question

Hi

I have a std::vectorstd::string parameter and I like to read the values getParam. How does the command line syntax look to read my names param from bash.

---

e.g. rosrun my_pgk my_node _names:=???????
I tried:
_names:="max susi"
_names:="max, susi"
_names:="[max, susi]"
_names:="(max, susi)"
nothing worked :-(

---

My code looks like this:

std::vector<std::string> names;
n_param_.getParam ( "names", names);

//For debugging
std::stringstream ss;
for ( size_t i = 0; i < names.size(); i++ ) ss << ( i!=0?", ":"" ) << names[i];
ROS_INFO ( "names: %s", ss.str().c_str() );

Greetings Markus

---

Originally posted by Markus Bader on ROS Answers with karma: 847 on 2014-10-09

Post score: 3

Answer 1

For the moment I solved the problem with a hack

std::string tmp;
std::vector<std::string> names;
n_param_.getParam ( "names", tmp);
boost::erase_all(tmp, " ");
boost::split ( names, tmp, boost::is_any_of(","));

now I can read it with _names:="max, susi"

---

Originally posted by Markus Bader with karma: 847 on 2014-10-10

This answer was ACCEPTED on the original site

Post score: 2

---

Original comments

Comment by gvdhoorn on 2018-01-28:
For Indigo and newer, please refer to @peci1's answer below.

Answer 2

Now on ROS Indigo, I can get the list to an argument as follows:

rosrun pkg node _param:="[1, 2]"

This will put a list with two numbers on the param server.

It seems to be documented here: http://wiki.ros.org/ROS/YAMLCommandLine . Strings would be quoted by the other type of quotes than the one used to quote the whole list.

In rospy, it works out of the box:

print rospy.get_param("~param")[0]

In roscpp, the use is also as easy as:

std::vector<double> v;
pnh.param("param", v, std::vector<double>());

Problems can arise when you want to pass the array to the node using a roslaunch file - then the clasical "<arg> and <param> policy" won't work, since roslaunch doesn't know about list types and will convert the list to a single string. Since Lunar, you may use the construct <param name="param" type="yaml" value="$(arg param)" /> (documentation). In Indigo, you can achieve a similar result by <rosparam param="param" subst_value="True">$(arg param)</rosparam> (documentation).

---

Originally posted by peci1 with karma: 1366 on 2018-01-25

This answer was NOT ACCEPTED on the original site

Post score: 7

---

Original comments

Comment by 2ROS0 on 2018-01-28:
<arg name="string_list" default="[this, is, list]"/> <rosparam param="string_list" subst_value="True">$(arg string_list)</rosparam>

This shows the following error: requires the 'string_list' arg to be set

Comment by peci1 on 2018-01-28:
@2ROS0 Which ROS version? Did you try enclosing each of the three strings in single quotes?

Comment by 2ROS0 on 2018-01-28:
kinetic, I defaulted to the hack in @Markus Bader answer. I think I did try with the quotes but I'll try again in a bit and edit this comment

Comment by 2ROS0 on 2018-01-28:
yeah I tried with the whitelist example on the documentation you linked as is without any changes. It gives the same answer even though those are ints and not strings

Comment by peci1 on 2018-01-29:
@2ROS0 So does it work for you in the end?

Comment by 2ROS0 on 2018-01-29:
No, it seems there is a bug somewhere. I removed everything else from my launchfile and tried with a simple image_view node as shown below but still same error. Is there someone that can check to see if the same error occurs to them? I am running ROS Kinetic

Comment by 2ROS0 on 2018-01-29:
Here is my basic launchfile:

   <arg name="whitelist" default="[3, 2]"/>

   <rosparam param="whitelist" subst_value="True">$(arg whitelist)</rosparam>

Comment by peci1 on 2018-01-29:
@2ROS0 The <arg> tag has to be a direct child of the <launch> element, and not inside the <node>. Then it will work.

Comment by 2ROS0 on 2018-01-29:
@peci1 you should add the launchfile syntax to the wiki page about reading ros params if you don't mind because it is missing there

Comment by Andrew Price on 2020-02-10:
Has anyone gotten the

<param type="yaml"/>

syntax to work? It fails for me on Kinetic with:

Invalid <node> tag: Invalid <param> tag: Unknown type 'yaml'. 

Param xml is <param name="ignore" type="yaml" value="$(arg ignore)"/>.

The rosparam version does work, though.