Load 2D parameter from parameter server

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Hi all,

I have a YAML file which successfully loads the following into the server:

        joints: [ [name_1_1, name_1_2], 
            [name_2_1, name_2_2], 
            [name_3_1], 
            [name_4_1, name_4_2], 
            [name_5_1, name_5_2], 
            [name_6_1, name_6_2] ]

But I am having problems writing the c++ to return the contents. For a 1D vector I can easily use:

std::vector<std::string> names;
nh.getParam("/joints", names);

where the YAML could be:

joints: [name_1, name_2, name_3]

To go 2D I tried to load it with:

std::vector< std::vector<std::string> > names;
nh.getParam("/joints", names);

But I get a build error:

no matching function for call to ‘ros::NodeHandle::getParam(const char [17], std::vector<std::vector<std::basic_string<char> > >&)’

How can I load 2D parameters from the ros parameter server in C++?

Thank you in advance.