Re: Dynamic menu

From:
cpp4ever <n2xssvv.g02gfr12930@ntlworld.com>
Newsgroups:
comp.lang.c++
Date:
Fri, 09 Jul 2010 20:48:16 +0100
Message-ID:
<42LZn.55567$cJ6.25869@hurricane>
On 07/09/2010 12:54 PM, Francesco S. Carta wrote:

Hi there,
in it.comp.lang.c++ somebody asked for directions (for a tutorial,
actually) about creating a menu in C++, and I've answered mentioning
pointers to functions and creating a simple example that accepts only
pointers to void functions taking no parameters.

Then I've started fiddling with the idea and I've implemented a more
complex version that accepts pointers to functions that take parameters
too, allowing the client code to pass any kind of function - with a
single parameter but without type restrictions, as the "add_item()"
method is a template).

Here below I paste the complete code with an usage example, I wonder if
there is any simpler way of achieving the same purposes, maybe without
using inheritance.

Any other suggestion or correction about my coding style will be
welcome, I completely avoided to add comments because the code should be
self-explaining even if a bit convoluted.

Thanks for your attention.

//-------
#include <iostream>
#include <typeinfo>
#include <vector>
#include <list>

class MenuItem {
public:
    MenuItem() {}
    virtual ~MenuItem() {}
    virtual void execute() {}
    virtual void display() {}
    virtual std::string caption() = 0;
    virtual std::string command() = 0;
    virtual MenuItem* parent() = 0;
};

class MenuItemContainer : public MenuItem {
    std::string _caption;
    std::string _command;
    MenuItem* _parent;

protected:
    friend class Menu;
    std::vector<MenuItem*> _items;

public:

    MenuItemContainer(std::string caption,
                      std::string command,
                      MenuItem* parent) :
            _caption(caption),
            _command(command),
            _parent(parent) {}

    std::string caption() {
        return _caption;
    }

    std::string command() {
        return _command;
    }

    MenuItem* parent() {
        return _parent;
    }
};

class MenuItemWithoutParam : public MenuItem {
    std::string _caption;
    std::string _command;
    MenuItem* _parent;
    void (*_callback)();

public:
    MenuItemWithoutParam(std::string caption,
                         std::string command,
                         MenuItem* parent,
                         void (*callback)()) :
            _caption(caption),
            _command(command),
            _parent(parent),
            _callback(callback) {}

    void execute() {
        if (_callback) {
            _callback();
        }
    }

    std::string caption() {
        return _caption;
    }

    std::string command() {
        return _command;
    }

    MenuItem* parent() {
        return _parent;
    }

};

template<class T> class MenuItemWithParam : public MenuItem {
    std::string _caption;
    std::string _command;
    MenuItem* _parent;
    void (*_callback)(T*);
    T* _param;

public:

    MenuItemWithParam(std::string caption,
                      std::string command,
                      MenuItem* parent,
                      void (*callback)(T*),
                      T* param) :
            _caption(caption),
            _command(command),
            _parent(parent),
            _callback(callback),
            _param(param) {}

    void execute() {
        if (_callback && _param) {
            _callback(_param);
        }
    }

    std::string caption() {
        return _caption;
    }

    std::string command() {
        return _command;
    }

    MenuItem* parent() {
        return _parent;
    }
};

class Menu {
    MenuItemContainer _basecontainer;
    std::istream& _input;
    std::ostream& _output;
public:
    Menu(std::istream& input,
         std::ostream& output) :
            _basecontainer("","",0),
            _input(input),
            _output(output) {}
    template<class T>
    MenuItem* add_item(std::string caption,
                       std::string command,
                       MenuItem* parent,
                       void (*callback)(T*),
                       T* param) {
        MenuItem* item;
        if (parent && typeid(*parent) == typeid(MenuItemContainer)) {
            MenuItemContainer* container
            = static_cast<MenuItemContainer*>(parent);
            item = new MenuItemWithParam<T>(caption,
                                            command,
                                            parent,
                                            callback,
                                            param);
            container->_items.push_back(item);
        } else {
            item = new MenuItemWithParam<T>(caption,
                                            command,
                                            &_basecontainer,
                                            callback,
                                            param);
            _basecontainer._items.push_back(item);
        }
        return item;

    }

    MenuItem* add_item(std::string caption,
                       std::string command,
                       MenuItem* parent,
                       void (*callback)()) {
        MenuItem* item;
        if (parent && typeid(*parent) == typeid(MenuItemContainer)) {
            MenuItemContainer* container
            = static_cast<MenuItemContainer*>(parent);
            item = new MenuItemWithoutParam(caption,
                                            command,
                                            parent,
                                            callback);
            container->_items.push_back(item);
        } else {
            _basecontainer._items.push_back(item);
        }
        return item;
    }

    MenuItem* add_item(std::string caption,
                       std::string command,
                       MenuItem* parent) {
        MenuItem* item;
        if (parent && typeid(*parent) == typeid(MenuItemContainer)) {
            MenuItemContainer* container
            = static_cast<MenuItemContainer*>(parent);
            item = new MenuItemContainer(caption,
                                         command,
                                         parent);
            container->_items.push_back(item);
        } else {
            item = new MenuItemContainer(caption,
                                         command,
                                         &_basecontainer);
            _basecontainer._items.push_back(item);
        }
        return item;
    }
    void interact() {
        std::string line;
        MenuItemContainer* current = &_basecontainer;
        MenuItem* selected;
        for (;;) {
            selected = 0;
            _output << "\n-------" << std::endl;
            for (size_t i = 0; i < current->_items.size(); ++i) {
                _output << "[" << current->_items[i]->command()
                << "] " << current->_items[i]->caption()
                << std:: endl;
            }
            if (current->parent()) {
                _output << "[up] Upper menu" << std::endl;
            }
            _output << "[exit] Exit program" << std::endl;
            _output << "Insert command:" << std::endl << ">";
            getline(_input, line);
            if (line == "up" && current->parent()) {
                current = static_cast<MenuItemContainer*>
                          (current->parent());
            } else if (line == "exit") {
                return;
            } else {
                for (size_t i = 0; i < current->_items.size(); ++i) {
                    if (current->_items[i]->command() == line) {
                        selected = current->_items[i];
                        break;
                    }
                }
            }
            _output << std::endl;
            if (selected) {
                if (typeid(*selected) == typeid(MenuItemContainer)) {
                    current = static_cast<MenuItemContainer*>
                              (selected);
                } else {
                    selected->execute();
                }
            } else {
                _output << "Unrecognized command" << std::endl;
            }
        }
    }
};

// client section

using namespace std;

Menu menu(cin, cout);

void increment(int* i) {
    ++*i;
}

void print(int* i) {
    cout << *i << endl;
}

void cite(string* str) {
    cout << *str << endl;
}

void addquote(MenuItem* parent) {
    static list<string> quotes;
    string caption;
    string command;
    string quote;
    cout << "Insert caption: " << endl;
    cout << ">";
    getline(cin, caption);
    cout << "Insert command: " << endl;
    cout << ">";
    getline(cin, command);
    cout << "Insert quote: " << endl;
    cout << ">";
    getline(cin, quote);
    if (caption != "" && command != "" && quote != "") {
        quotes.push_back(quote);
        menu.add_item(caption, command, parent, cite, &quotes.back());
    } else {
        cout << "Unable to create quote"
        << " please retry and fill in all fields" << endl;
    }
}

int main() {
    int i = 42;
    MenuItem* program = menu.add_item("Program", "p", 0);
    MenuItem* variable = menu.add_item("Variable", "v", program);
    MenuItem* quotes = menu.add_item("Quotes", "q", program);
    menu.add_item("Increment", "i", variable, increment, &i);
    menu.add_item("Print", "p", variable, print, &i);
    string hello = "Hello world!";
    string panic = "Don't panic!";
    menu.add_item("Add quote", "a", quotes, addquote, quotes);
    menu.add_item("Hello", "h", quotes, cite, &hello);
    menu.add_item("H2G2", "42", quotes, cite, &panic);
    menu.interact();
    return 0;
}
//-------


IMHO I think use of inheritance is better than using callback functions.
Each derived menuitem type then has it's own private properties that in
turn can be accessed by descendant classes via protected functions. This
provides far greater flexibility IMHO, and
is easier to implement and understand.

HTH

cpp4ever

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