Can't pass in a numerical string as arg param to C++ node

[lucasw]

If a numerical string like "4235" or "57.23" is set onto the parameter server as a command line argument to a C++ node then it is turned into type int or float on the parameter server and a getParam of type string will not get it.

#include <ros/ros.h>

int main(int argc, char** argv)
{
  ros::init(argc, argv, "string_param_test");
  ros::NodeHandle nh("~");

  // this comes up blank if str_param was passed in as argument, or set
  // rosparam set /string_param_test/str_param "98432"
  // the type is int so a string getParam fails.
  std::string test = "";
  nh.getParam("str_param", test);
  std::cout << test << "\n";

  // this works as desired
  nh.setParam("str_param2", "12345");
  nh.getParam("str_param2", test);
  std::cout << test << "\n";

  return 0;
}

$ rosrun param_test string_param_test _str_param:="98432"

12345

$ rosparam get /string_param_test/str_param2
'12345'

It looks like the root of the issue is that setting a parameter with quotes that is a valid int or float turns into an int or float:

$ rosparam set /string_param_test/str_param '8945'
$ rosparam get /string_param_test/str_param 
8945

I'm using kinetic on Ubuntu 16.04.

I also tried this with kinetic-devel, though got a ‘ros_steadytime’ is not a member of ‘ros’ error (even when bringing in the latest roscpp_core) so went back to d4788bc .

(I experimented with adding unit tests here but I'm not sure how to quickly build and test them in a catkin tools build environment - it takes a long time to build and run many tests of test_roscpp, I can't selectively just do a few. How to build just ./devel/lib/test_roscpp/test_roscpp-params and not run it or anything else? Extract the build line out of a verbose build/run of everything?)

[lucasw]

Double quotes with single inner quotes works for rosparam set, the outer quotes are stripped of, and the inner quotes clue rosparam that the type is string:

rosparam set /test "'98432'"
rosparam get /test 
'98432'

But using that as an arg to a C++ node and the string is '98432', with the single quotes as characters in the string, but in a python node the quotes are stripped and the type is correctly determined to be a string.

rosparam get on a string with single quotes yields

'''98432'''

#!/usr/bin/env python

import rospy

rospy.init_node("string_param_test")
val = rospy.get_param("~str_param", None)
print val, type(val)

$ rosparam set /string_param_test/str_param "'4325'"
$ rosrun param_test string_param_test.py
4325 <type 'str'>

$ rosrun param_test string_param_test.py _str_param:="'4325'"
4325 <type 'str'>

$ rosrun param_test string_param_test.py _str_param:='"4325"'
4325 <type 'str'>

rosrun param_test string_param_test.py _str_param:="4325"
4325 <type 'int'>

[lucasw]

Double + single quotes doesn't work for roslaunch <param> tags (regardless if the node using the param is C++ or python), the inner single quotes become part of the string as with args to a C++ node.

(type="str" works fine but that isn't available outside of roslaunch)

[gavanderhoorn]

I don't see it in your example invocations, but is '"12345"' also problematic? The ' should prevent the shell from evaluating the argument, so I would expect the " to be preserved.

[lucasw]

'"12345"' results in 12345 of type string when given to rosparam set or rospy arg so my pr makes C++ and roslaunch args match that.

Would the argument for going the other way and making '"12345"' preserve the inner quotes in all cases be that there isn't otherwise a good way to set a string with quotes around it?

With some further experiments with quotes within strings it looks like there is an additional issue:

$ rosparam set /foo "'foo' blah" 
Traceback (most recent call last):
  File "/opt/ros/kinetic/bin/rosparam", line 35, in <module>
    rosparam.yamlmain()
  File "/opt/ros/kinetic/lib/python2.7/dist-packages/rosparam/__init__.py", line 626, in yamlmain
    _rosparam_cmd_set_load(command, argv)
  File "/opt/ros/kinetic/lib/python2.7/dist-packages/rosparam/__init__.py", line 543, in _rosparam_cmd_set_load
    set_param(name, arg2, verbose=options.verbose)
  File "/opt/ros/kinetic/lib/python2.7/dist-packages/rosparam/__init__.py", line 375, in set_param
    set_param_raw(param, yaml.load(value), verbose=verbose)
  File "/usr/lib/python2.7/dist-packages/yaml/__init__.py", line 71, in load
    return loader.get_single_data()
  File "/usr/lib/python2.7/dist-packages/yaml/constructor.py", line 37, in get_single_data
    node = self.get_single_node()
  File "/usr/lib/python2.7/dist-packages/yaml/composer.py", line 39, in get_single_node
    if not self.check_event(StreamEndEvent):
  File "/usr/lib/python2.7/dist-packages/yaml/parser.py", line 98, in check_event
    self.current_event = self.state()
  File "/usr/lib/python2.7/dist-packages/yaml/parser.py", line 174, in parse_document_start
    self.peek_token().start_mark)
yaml.parser.ParserError: expected '<document start>', but found '<scalar>'
  in "<string>", line 1, column 7:
    'foo' blah

rosparam set /foo '"foo" blah' is the same, but putting quotes later than the first non-space character works:

$ rosparam set /foo 'blah "foo"' && rosparam get /foo
blah "foo"

So there is some code (in yaml parser not rospy?) that is looking for a leading quote regardless of a matching ending quote and then misinterprets and throws.

Escaping the space and no outer quotes succeeds but loses the quotes:

rosparam set /foo '1234'\ blah  && rosparam get /foo
1234 blah

rosparam get could be losing quotes that rosparam set preserved, I'll have to look at that later.

[gavanderhoorn]

Strings in yaml don't necessarily need quotes. That is probably why you don't see them in rosparam get output.

Not seeing quotes also doesn't necessarily mean it's not a string.

[lucasw]

Not seeing quotes also doesn't necessarily mean it's not a string.

I've noticed that rosparam prints quotes when it it is ambiguous: 1234 type string prints '1234', but 1234x is just plain 1234x.

-p pretty print drops the quotes.

(It would be convenient if -v printed the type definitively for what is in the rosparam server, I could add that later)

[flixr]

We are encountering the same problem...

[VictorLamoine]

For those looking for a work-around:

std::string serial_number;
if (!nh->getParam("connect_serial_number", serial_number))
{
  // When using rosrun the serial number is interpreted as an int and
  // can't be forced into a string. See https://github.com/ros/ros_comm/issues/1339
  int serial_number_int;
  if (nh->getParam("connect_serial_number", serial_number_int))
    serial_number = std::to_string(serial_number_int);
}

First: try to get the parameter as a string.
If it fails: try to get the parameter as an int and convert it to a string.
With this it's pretty easy to support integers/floats.

Then you can run the node and pass the argument as you would expect:

rosrun my_package my_node _connect_serial_number:=190345

[flixr]

yeah, but that workaround has limitations... e.g. it won't work for strings with leading zeros..