Function with object as argument, as argument of another function

Question

I have troubles fixing a little problem I have. I have two classes. One is called MenuBar, in this class there is a vector array of the other object (MenuOption). MenuBar contains a method that create a new MenuOption and add it to the array. The constructor of MenuOption needs two arguments: a string(for the name) and a function(the action that this option performs). I want the function received to be of that form:

void method(SDL_Surface* arg1, MenuBar* arg2);

So I repaired the double inclusion problem by adding "class MenuBar;" just after my #include "MenuBar.h". But I still have an error, it says "error: invalid use of void expression" at the line I marked in the below code of main.cpp.

Now my complete code looks like that:

main.cpp

void connect(SDL_Surface* arg1, MenuBar* arg2);
void about(SDL_Surface* arg1, MenuBar* arg2);

int main()
{
    SDL_Surface* screen;
    MenuBar menu(/*initialization*/);
    menu.addOption("Connect",connect(screen,&menu));//<---------
    menu.addOption("About",about(screen,&menu));    //<---------
}

void connect(SDL_Surface* arg1, MenuBar* arg2)
{...}

void about(SDL_Surface* arg1, MenuBar* arg2)
{...}

MenuBar.h

#include "MenuOption.h"
class MenuBar
{
    public:
        ...
        void addOption(string optionName,void (*f)(SDL_Surface*, MenuBar*) );
    private:
        vector<MenuOption> optionList;
}

MenuBar.cpp

void MenuBar::addOption(string optionName,void (*f)(SDL_Surface*, MenuBar*) )
{
    MenuOption tempOption(optionName,f);
    optionList.push_back(tempOption);
}

MenuOption.h

#include "MenuBar.h"
class MenuBar;

class MenuOption
{
    public:
        MenuOption(string optionName,void (*f)(SDL_Surface*, MenuBar*) );
        void (*run)(SDL_Surface*, MenuBar*);
    private:
        string name;
}

MenuOption.cpp

MenuOption::MenuOption(string optionName,void (*f)(SDL_Surface*, MenuBar*) )
{
    name = optionName;
    run = f;
}

Thanks for the help!

Philou231

Tushar · Accepted Answer · 2013-03-30 05:05:02Z

1

menu.addOption("Connect",connect(screen,&menu));

You're passing the result of connect, which is void, as the second parameter to addOption. Try:

menu.addOption("Connect",connect);

--

I think you're looking to send both a function and some parameters for that function, so consider adding two extra parameters to addOption such that it's signature is like:

addOption(string optionName,void (*f)(SDL_Surface*, MenuBar*), SDL_Surface*, MenuBar*)

And call f with the parameters given inside addOption. Then you call addOption like so:

menu.addOption("Connect",connect, screen, &menu);

answered Mar 30, 2013 at 5:05

Tushar

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1 Comment

Philou231 Over a year ago

Wow! Now it makes a lot of sens, thanks a lot. It is working perfectly. I got confused because I didn't remember I had that run function, and this was the function supposed to get the parameters.

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