From a MessageDialog how to read variables when i use pango markup?

how to use pango markup in messagedialog text using variable

For example this code

void usb_boot::creation(){
//Gtk::MessageDialog dialogue(*this, listeDeroulante.get_active_text());
std::string message("Type de formatage : " + type), type1, chemin1;
Gtk::MessageDialog *dialogue = new Gtk::MessageDialog("Résumé", true, Gtk::MESSAGE_QUESTION, Gtk::BUTTONS_YES_NO);
dialogue->set_title("Résumé");
dialogue->set_message("<span weight='bold'>message</span>",true);
dialogue->set_secondary_text("<b>listeDeroulante.get_active_text()</b>", true);
dialogue->set_default_response(Gtk::RESPONSE_YES);
int result = dialogue->run();

set_message and set_secondary_text have to print variables but just "see" word. Is there a way to read like variables ?

While the std::stringstream solution works, I would suggest using simple string concatenation, through std::string's operator+:

#include <gtkmm.h>

int main(int argc, char **argv)
{
    auto app = Gtk::Application::create(argc, argv, "so.question.q63886899");
    
    Gtk::Window w;
    w.show_all();

    {
        // Unformatted messages:
        std::string primaryMessage = "Some message...";
        std::string secondaryMessage = "Some more message details...";

        Gtk::MessageDialog dialog(w, "Message dialog", true, Gtk::MESSAGE_QUESTION, Gtk::BUTTONS_YES_NO);
        dialog.set_title("Title");

        // Add pango markup tags through string concatenation:
        dialog.set_message("<span weight='bold'>" + primaryMessage + "</span>", true);
        dialog.set_secondary_text("<b>" + secondaryMessage + "</b>", true);

        dialog.run();
    }

    return app->run(w);
}

With this solution, no need to introduce an extra type.