[Discuss-gnuradio] Output block: vector of a vector

Hi,
I'm wondering if it is possible to make an output of a block that is a vector of a vector.
I tried with:

    int
    vector_source_tagged_impl::work(int noutput_items,
        gr_vector_const_void_star &input_items,
        gr_vector_void_star &output_items)
    {


      std::vector<int> *optr = (std::vector<int> *) output_items[0];

and there are not compiling errors, but when I run GRC, it stops with this:

Executing: /usr/bin/python -u /home/alice/project_GNURADIO/tx_ofdm.py

Using Volk machine: avx2_64_mmx_orc

>>> Done

Any suggestions?
Thanks in advance.

Alice