Providing initial text for the readline buffer

In a readline buffer I want to provide an initial value the user can edit. This can either be a default value or the old value of the field already saved to my database. The entered value shall not be added to the readline-history as it is only "data" not a command.

From the samples here and on the internet I have learned that this code should do the job:

char *deftext;

int MatCustom::set_deftext ()
{
    // cout << "set_deftext called ... deftext: " << deftext << endl;
    if (deftext)
    {
        // cout << "inserting..." << endl;
        rl_insert_text(deftext);
        // rl_line_buffer = deftext;
        // cout << rl_stuff_char('J') << endl;
        rl_redisplay();

        deftext = (char *)NULL;

        rl_startup_hook = (rl_hook_func_t *)NULL;
        // rl_pre_input_hook = (rl_hook_func_t *)NULL;
    };
    return 0;
}

string MatCustom::getlineWithoutHistory(const string &field) {
    string returnString;
    const char *buffer;
    char *cstr = new char[field.length() + 1];
    strcpy(cstr, field.c_str());

    deftext = cstr;
    // cout << "Deftext in getLineWithoutHistory: " << deftext << endl;
    rl_startup_hook = set_deftext;
    // rl_pre_input_hook = set_deftext;

    buffer = :: readline("");

    if (buffer != nullptr) {
        returnString = buffer;
    } else {
        returnString = "";
    }
    free((void *) buffer);
    delete [] cstr;

    return returnString;
}

It works perfectly well to convert my old value to a char* and pass it to the global variable deftext, because a parameter cannot be given to the readline-hook-functions.

I am experiencing problems: Whenever I use the rl_startup_hook, which is said to be called before the prompt gets printed, I find this this hook never gets executed. However, when I use the rl_pre_input_hook, which is called prior to the input to begin, my function set_deftext actually gets called. This functions finds deftext set.

Still, I don't get any text inserted into the input buffer. The function rl_insert_text produces no change – even when I use rl_redisplay(). Directly changing the buffer with rl_line_buffer = deftext; also has no effect. When I try cout << rl_stuff_char('J') << endl; for debugging just to insert a single char, nothing happens and the function returns 0 indicating an unsuccessful insert.

Both functions are static member functions. I usually call my function with

input = MatCustom::getlineWithoutHistory(rawValue);

to edit to provided value (rawValue).