Problem changing wxComboBox width

[David Carr]

Here is an minimal example of what I have.  How should I change this so
that the wxComboBox is just wide enough to fit the text?  In my actual
application, there are several other widgets in the same sizer with the
wxComboBox.

    wxPanel* root = new wxPanel(this, -1);
    wxBoxSizer* root_sizer = new wxBoxSizer(wxHORIZONTAL);

    wxComboBox* cb = new wxComboBox(root, -1, wxT("Text"),
					    wxDefaultPosition,
					    wxDefaultSize);
    cb->SetSize(100,-1); //try to change the width

    root_sizer->Add(cb, 0);

    root->SetSizer(root_sizer);

Thanks for the help,
David Carr