Function Pointers in C++ Class Files - class

Question

I've been trying to work with function pointers for quite a bit now, and to no avail. I've been working with a few friends to create a C++ 11 library to make creating ASCII games easier, and I've personally been working on creating a menu class. The beef of the class is complete, but one issue - I can't get the buttons to call functions. I always get the error:
terminate called after throwing an instance of 'std::bad_function_call'
what(): bad_function_call
This application has requested the Runtime to terminate it in an unusual way.
Please contact the application's support team for more information.
Obviously the error lies somewhere in the pointers, but I can't solve it for the life of me. Thanks for the help in advance.
Menu.h
#ifndef MENU_H
#define MENU_H
using namespace std;
#include <functional>
#include <string>
#include <map>
class Menu {
public:
int numberOfOptions;
map<int, string> options;
int currentSelection;
string title;
Menu();
Menu(int initialNumberOfOptions, map<int, string> initialOptions, int initialSelection);
void display();
void waitForInput();
void attachOptionAction(int option, void (*function)());
private:
map<int, void (*std::function<void()>)> optionActions;
void executeOptionAction(int option);
};
#endif
Menu.cpp
#include "Menu.h"
#include <windows.h>
#include <iostream>
#include <conio.h>
Menu::Menu(int initialNumberOfOptions, map<int, string> initialOptions, int initialSelection) {
title = "";
numberOfOptions = initialNumberOfOptions;
options = initialOptions;
currentSelection = initialSelection;
}
void Menu::display() {
SetConsoleCursorPosition(GetStdHandle(STD_OUTPUT_HANDLE), {0, 0});
for(int i = 0; i < 10; i++) {
cout << " " << endl;
}
SetConsoleCursorPosition(GetStdHandle(STD_OUTPUT_HANDLE), {0, 0});
if(title != "") {
cout << title << endl << endl;
}
for(int i = 0; i < numberOfOptions; i++) {
if(i == currentSelection - 1) {
cout << "[ " << options[i] << " ]" << endl;
} else {
cout << options[i] << endl;
}
}
waitForInput();
}
void Menu::waitForInput() {
char input;
while(!kbhit());
input = getch();
if(input == 72 && currentSelection > 1) {
currentSelection--;
} else if (input == 80 && currentSelection < numberOfOptions) {
currentSelection++;
} else if (input == 13) {
if(currentSelection == 1) {
executeOptionAction(1);
}
return;
}
display();
}
void Menu::attachOptionAction(int option, std::function<void()> function) {
optionActions[option] = function;
}
void Menu::executeOptionAction(int option) {
(optionActions[option])();
}
test.cpp
#include "Menu.h"
#include <unistd.h>
#include <iostream>
#include <iomanip>
#include <map>
void test() {
cout << "Hello, World!";
}
int main() {
map<int, string> options;
options[0] = "Play";
options[1] = "Help";
options[2] = "Quit";
Menu menu(3, options, 1);
menu.title = "ASCII Game Library 2015";
menu.display();
void (*actionPointer)() = NULL;
menu.attachOptionAction(1, (*actionPointer));
return 0;
}

Answer 1

This is wrong. I'm not even sure what's that supposed to be.
map<int, void (*std::function<void()>)> optionActions;
It should be:
map<int, std::function<void()>> optionActions;
This here is also wrong. It would be correct if you hadn't imported std into your current namespace.
void attachOptionAction(int option, void (*function)());
It should be:
void attachOptionAction(int option, const std::function<void()> & action);
This here is also wrong. You can't name your argument function after you imported std into your namespace.
void Menu::attachOptionAction(int option, std::function<void()> function)
It should be:
void Menu::attachOptionAction(int option, const std::function<void()> & action)
This here is also wrong. You don't check if the function exists or that a valid function pointer was assigned to it. Which you haven't.
(optionActions[option])();
It should be:
// Attempt to find the action!
map<int, std::function<void()>>::iterator action = optionActions.find(option);
// Did we find anything?
if (action == optionActions.end())
{
return;
}
// Is the function assigned to this action valid?
if (action->second)
{
action->second();
}
You are attaching a null function pointer to an action and try to call it. And since there's no validation it does exactly that. Which is why you get that exception:
void (*actionPointer)() = NULL;
menu.attachOptionAction(1, (*actionPointer));
But I'm not even sure how even managed to compile it :/
EDIT:
I hope you can find this example to be informative on what you're looking for.
#include <map>
#include <string>
#include <cstdlib>
#include <iostream>
#include <functional>
class Menu
{
protected:
typedef std::function<int (Menu &)> Callback;
typedef std::map<int, Menu> SubMenus;
public:
Menu()
: m_Id(0), m_Name(""), m_Handler(nullptr)
{
}
Menu(int id, const std::string & name, Callback clbk)
: m_Id(id), m_Name(name), m_Handler(clbk)
{
}
Menu & operator [] (int id)
{
return m_Childrens.at(id);
}
int Enter()
{
int result = 0;
if (m_Handler)
result = m_Handler(*this);
return result;
}
void Insert(const Menu & menu)
{
m_Childrens[menu.m_Id] = menu;
}
void Insert(int id, const std::string & name, Callback clbk)
{
m_Childrens[id] = Menu(id, name, clbk);
}
void Remove(int id)
{
m_Childrens.erase(id);
}
int GetId() const
{
return m_Id;
}
const std::string & GetName() const
{
return m_Name;
}
const Callback & GetHandler() const
{
return m_Handler;
}
bool IsChildren(int id) const
{
return (m_Childrens.find(id) != m_Childrens.cend());
}
Menu & GetChildren(int id)
{
return m_Childrens.at(id);
}
const SubMenus & GetChildrens() const
{
return m_Childrens;
}
private:
int m_Id;
std::string m_Name;
Callback m_Handler;
SubMenus m_Childrens;
};
void ClearScreen()
{
system("cls");
}
int SharedMenuDisplay(const Menu & menu)
{
ClearScreen();
std::cout << "Welcome to " << menu.GetName() << std::endl;
for (const auto & m : menu.GetChildrens())
{
std::cout << "> " << m.second.GetId() << " - " << m.second.GetName() << std::endl;
}
std::cout << "> 0 - Go Back" << std::endl;
std::cout << "Please select a sub menu: ";
int choice;
std::cin >> choice;
return choice;
}
int Menu_Home(Menu & menu)
{
int choice;
int result = 0;
do {
ClearScreen();
std::cout << "Welcome to " << menu.GetName() << std::endl;
for (const auto & m : menu.GetChildrens())
{
std::cout << "> " << m.second.GetId() << " - " << m.second.GetName() << std::endl;
}
std::cout << "> 0 - To Leave" << std::endl;
std::cout << "Please select a sub menu: ";
std::cin >> choice;
if (choice != 0 && menu.IsChildren(choice))
result = menu.GetChildren(choice).Enter();
} while (choice != 0);
return result;
}
int Menu_A(Menu & menu)
{
int choice;
int result = 0;
do {
choice = SharedMenuDisplay(menu);
if (choice != 0 && menu.IsChildren(choice))
result = menu.GetChildren(choice).Enter();
} while (choice != 0);
return result;
}
int Menu_A_SubMenu_X(Menu & menu)
{
ClearScreen();
std::cout << "You have selected " << menu.GetName() << std::endl;
std::cout << "> Type something and press Enter to go back..." << std::endl;
std::string str;
std::cin >> str;
return 0;
}
int Menu_A_SubMenu_Y(Menu & menu)
{
ClearScreen();
std::cout << "You have selected " << menu.GetName() << std::endl;
std::cout << "> Type something and press Enter to go back..." << std::endl;
std::string str;
std::cin >> str;
return 0;
}
int Menu_A_SubMenu_Z(Menu & menu)
{
ClearScreen();
std::cout << "You have selected " << menu.GetName() << std::endl;
std::cout << "> Type something and press Enter to go back..." << std::endl;
std::string str;
std::cin >> str;
return 0;
}
int Menu_B(Menu & menu)
{
int choice;
int result = 0;
do {
choice = SharedMenuDisplay(menu);
if (choice != 0 && menu.IsChildren(choice))
result = menu.GetChildren(choice).Enter();
} while (choice != 0);
return result;
}
int Menu_B_SubMenu_X(Menu & menu)
{
ClearScreen();
std::cout << "You have selected " << menu.GetName() << std::endl;
std::cout << "> Type something and press Enter to go back..." << std::endl;
std::string str;
std::cin >> str;
return 0;
}
int Menu_B_SubMenu_Y(Menu & menu)
{
ClearScreen();
std::cout << "You have selected " << menu.GetName() << std::endl;
std::cout << "> Type something and press Enter to go back..." << std::endl;
std::string str;
std::cin >> str;
return 0;
}
int Menu_B_SubMenu_Z(Menu & menu)
{
ClearScreen();
std::cout << "You have selected " << menu.GetName() << std::endl;
std::cout << "> Type something and press Enter to go back..." << std::endl;
std::string str;
std::cin >> str;
return 0;
}
int Menu_C(Menu & menu)
{
ClearScreen();
std::cout << "You have selected " << menu.GetName() << std::endl;
std::cout << "> Type something and press Enter to go back..." << std::endl;
std::string str;
std::cin >> str;
return 0;
}
int main(int argc, char **argv)
{
Menu home(-1, "Home", &Menu_Home);
home.Insert(1, "Menu Item A", &Menu_A);
home.Insert(2, "Menu Item B", &Menu_B);
home.Insert(3, "Menu Item C", &Menu_C);
home.GetChildren(1).Insert(1, "Sub Menu Item X", &Menu_A_SubMenu_X);
home.GetChildren(1).Insert(2, "Sub Menu Item Y", &Menu_A_SubMenu_Y);
home.GetChildren(1).Insert(3, "Sub Menu Item Z", &Menu_A_SubMenu_Z);
home[2].Insert(1, "Sub Menu Item X", &Menu_B_SubMenu_X);
home[2].Insert(2, "Sub Menu Item Y", &Menu_B_SubMenu_Y);
home[2].Insert(3, "Sub Menu Item Z", &Menu_B_SubMenu_Z);
return home.Enter();
}