CODEWITHSUNDEEP
c++dictionarypointer-to-member
georgbüchner
georgbüchner

Reputation: 33

c++ calling function when using map of function pointer

I set up this account mainly because I couldn't find answers elsewhere. I checked, various tutorials or questions/ answers on stackoverflow and different pages.

I'm programming a terminal based textadventure and need a map of functions. This is what I got (I left out all the stuff that isn't of interesting for the problem)

#include <map>

using namespace std;

class CPlayer
{
private:

    //Players functions:
    typedef void(CPlayer::*m_PlayerFunction)(void); //Function-pointer points to various player 
                                                    //functions
    map<char*, m_PlayerFunction> *m_FunctionMap;    //Map containing all player functions

public:
    //Constructor
    CPlayer(char* chName, CRoom* curRoom, CInventory* Inventory);


    //Functions:
    bool useFunction(char* chPlayerCommand);
    void showDoors(); //Function displaing all doors in the room
    void showPeople(); //Function displaying all people in the room


};

#endif

#include "CPlayer.h"
#include <iostream>


CPlayer::CPlayer(char chName[128], CRoom* curRoom, CInventory *Inventory)
{
    //Players functions
    m_FunctionMap = new map<char*, CPlayer::m_PlayerFunction>;
    m_FunctionMap->insert(std::make_pair((char*)"show doors", &CPlayer::showDoors));
    m_FunctionMap->insert(std::make_pair((char*)"show people", &CPlayer::showPeople));
}






//Functions

//useFunction, calls fitting function, return "false", when no function ist found
bool CPlayer::useFunction(char* chPlayerCommand)
{
    CFunctions F;
    map<char*, m_PlayerFunction>::iterator it = m_FunctionMap->begin();

    for(it; it!=m_FunctionMap->end(); it++)
    {
        if(F.compare(chPlayerCommand, it->first) == true)
        {
            cout << "Hallo" << endl;
            (it->*second)();
        }
    }

    return false;
}

Now, the problem is the following:

If I call the function this way: (it->*second)(); which seems to be how it is supposed to be done, I get the following error: error: ‘second’ was not declared in this scope

If I call the function this way: (*it->second)(); which is what I got from this thread: Using a STL map of function pointers, I get following error: error: invalid use of unary ‘ * ’ on pointer to member

I'd be very glad if someone could help me. Thanks ahead for all the upcoming answers.

PS: It would also be interesting to know whether "map" or "unordered_map" is the better way of solving this problem.

As I said, thanks ahead: GB

Upvotes: 3

Views: 2580

Answers (1)

Ghislain Fourny
Ghislain Fourny

Reputation: 7279

The difficulty may be that it is at the same time a map, and it involves pointer-to-members, which makes the syntax to invoke more complicated with lots of parentheses that must be at the right positions. I think it should be something like this:

(this->*(it->second))()

Alternatively, as Rakete1111 points out, the following works as well:

(this->*it->second)()

(Note that the latter is less verbose, but also less easy to read for people who do not have the operator precedence on the top of their minds).

Upvotes: 2

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