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setting a param from the launch file doesn't work with string

asked 2014-09-24 03:23:24 -0500

MosheS gravatar image


I'm trying to set a param using the launch file like so:

<node name="right_sensor" pkg="action" type="input_signal" output="screen" >
    <param name="port" value="55551" />
    <param name="signal_name" value="right" />

In my code I have this:

  string port, signal_name;

  ros::NodeHandle private_node_handle_("~");
  private_node_handle_.param("signal_name", signal_name, string("signal"));
  private_node_handle_.param("port", port, string("55555"));

  ROS_INFO("PORT: %s", port.c_str());
  ROS_INFO("Signal Name: %s", signal_name.c_str());

It appears that the "port" is not transferred correctly (I get "55555").

Only "signal_name" is correct.

BTW, if I add a letter before the value of the param in port (e.g. "a55551), it will be ok.

Can anyone assist? Is this a bug or a feature?


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Did you try setting the type in the launch file with type="string"?

BennyRe gravatar image BennyRe  ( 2014-09-24 04:14:36 -0500 )edit

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answered 2014-09-24 12:01:31 -0500

bvbdort gravatar image

updated 2014-09-24 12:03:03 -0500

55551 will be resolved to integer and port is expecting string, so port is getting default value. Specifying the type attribute will solve it.

From wiki roslaunch XML param

If you don't specify the type, roslaunch will attempt to automatically determine the type. These rules are very basic:

numbers with '.'s are floating point, integers otherwise;

"true" and "false" are boolean (not case-sensitive).

all other values are strings

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Just to complement, adding type="string" to the launch file solves the problem when you set the parameter in that file. However, if you don't, the default value will be used. Hence, you could also explicitly call private_node_handle_.param<string>(...) to guarantee type safety at compile time.

Murilo F. M. gravatar image Murilo F. M.  ( 2014-09-24 16:56:03 -0500 )edit

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Asked: 2014-09-24 03:23:24 -0500

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Last updated: Sep 24 '14