Create a std::vector of msgs

edit

To create a vector of messages use

std::vector < parse_and_pub::LookuptableConstPtr> tables;

to populate the look up table use

tables.at(<index>).LuT.push_back(<value>);

Your message contains an array, so you do not need to create and array your self. If you have instantiated it, it already contains the array (which for C++ is serialized as std::vector). Use it like:

parse_and_pub::Lookuptable your_msg_obj;  // declare message instance

// fill lookup table
for ( /* all the values you want to add */ )
{
    your_msg_obj.LuT.push_back( 12.5 /* or whatever double value */ ); 
                          //  your_msg_obj.LuT is of type std::vector<double>
                          //  just treat it like you would thread any other vector of that kind 
                          //     i. e. use .resize(), .push_back(), operator[] on it or 
                          //                   derive iterators on it as you like
}

// and publish your message with filled look up table vector
your_publisher.publish( your_msg_obj );

Update for your comment:

For creating an array of msgs you can do:

std::vector<parse_and_pub::Lookuptable> your_luts;

your_luts.resize(1);
your_luts[0].LuT.push_back( 12.5 );

However, you won't be able to publish such a vector (also not if you use share_ptrs to messages). If you want to publish an arrary of such look up tables you must have another message type containing an array of your lookup tables:

Your Lookuptable.msg:

float64[] Lut

Your 2nd LookuptablesArray.msg:

parse_and_pub/Lookuptable[] look_up_tables ## array of Lookuptable.msg

Then you could create an instance of parse_and_pub::LookuptablesArray fill that and publish that.