C++ Calling Functions from an Array of Function Pointers

Question

I'm using function pointers stored in an array with a typedef defining the pointer and I'm a little lost on how I'm supposed to call the function.

here's the Menu.h part:

typedef void( Menu::*FunctionPointer )();

FunctionPointer* m_funcPointers;

here's the Menu.cpp part:

Menu::Menu()
    : m_running( true )
    , m_frameChanged( true )
    , m_currentButton( 0 )
    , m_numOfButtons( k_maxButtons )
    , m_menuButtons( new MenuButton[k_maxButtons] )
    , m_nullBtn( new MenuButton( "null", Vector2( -1, -1 ) ) )
    , m_frameTimer( 0 )
    , m_funcPointers( new FunctionPointer[k_maxButtons])
{
    m_timer.start();
    clearButtons();
    mainMenu();
}

void Menu::enterButton()
{
    m_funcPointers[m_currentButton]();//Error here
}

void Menu::mainMenu()
{
    m_funcPointers[0] = &Menu::btnPlay;
    m_menuButtons[0] = MenuButton("Play", Vector2(0, 0));

    m_funcPointers[1] = &Menu::btnHiScores;
    m_menuButtons[1] = MenuButton("HiScores", Vector2(0, 1));

    m_funcPointers[2] = &Menu::btnExit;
    m_menuButtons[2] = MenuButton("Exit", Vector2(0, 2));
}
void Menu::btnPlay()
{
    StandardGame* game = new StandardGame();

    game->play();

    delete game;
}

m_currentButton is an integer used as the index. I'm not sure how to actually call the function as the above line gives me this error:

**C2064 term does not evaluate to a function taking 0 arguments**

and visual studio give me this :

expression preceding parentheses of apparent call must have (pointer-to-) function type

I don't know how to solve the above problem and whether it's due to how I'm calling the function or how I'm storing it. Thanks in advance.

Welcome! Please take the tour first! Then, concerning your problem, please do some research up front, like e.g. using the error message in a websearch. If that doesn't turn up anything, extract a minimal reproducible example please so people don't have to guess what the rest of the code looks like. — Ulrich Eckhardt
– Ulrich Eckhardt, Commented Oct 22, 2018 at 17:32
@UlrichEckhardt I have done a fair bit of googling and can't figure out the problem but I can give more code if you want? — Will Anderson
– Will Anderson, Commented Oct 22, 2018 at 17:33
Please read the given link. You need to understand what MCVE means and then extract that from your code. — Ulrich Eckhardt
– Ulrich Eckhardt, Commented Oct 22, 2018 at 17:35
Thank you for the edit. Now the things are much clearer and the first answer is already there. A small improvement suggestion still: could you indicate in the code snippet the line of the error message (ok, it's easy to guess, but it would allow quicker answer and avoid downvotes from upset readers ;-) ) ? — Christophe
– Christophe, Commented Oct 22, 2018 at 17:45

eerorika · Accepted Answer · 2018-10-22 17:44:25Z

3

Calling Functions from an Array of Function Pointers

You call a function pointer in an array the same way as you would call a function that is not in an array.

Your problem isn't how to call a function pointer in an array as such. Your problem that you're trying to call a member function pointer as if it were a function pointer.

You can call a member function pointer like this:

Menu menu; // you'll need an instance of the class
(menu.*m_funcPointers[m_currentButton])();

Edit for the new example code: Since you're in a member function, perhaps you intend to call the member function pointer on this:

(this->*m_funcPointers[m_currentButton])();

If you find the syntax painful to read, I won't blame you. Instead, I'll suggest using std::invoke instead (available since C++-17):

std::invoke(m_funcPointers[m_currentButton], this);

edited Oct 22, 2018 at 17:44

answered Oct 22, 2018 at 17:37

eerorika

240k13 gold badges212 silver badges354 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Will Anderson Over a year ago

Thank you this is perfect, you edited just as I was about to ask whether I could use the this keyword.

Collectives™ on Stack Overflow

C++ Calling Functions from an Array of Function Pointers

1 Answer 1

1 Comment

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

1 Comment

Your Answer

Sign up or log in

Post as a guest

Linked

Related