Thread: More help on pointer to function in map

I am having difficulty with the syntax for calling a pointer to a function in a map.

Code:

vector<string*> * BeverageUserInterface::ParseMessage(vector<string*>* MessageIn)
{
   vector<string *>::iterator CommandPos;
   BeverageDriverMap::iterator CommandLookUp;
   
   for (CommandPos = (*MessageIn).begin(); CommandPos != (*MessageIn).end(); ++CommandPos)
   {
   	   CommandLookUp = BeverageDriverTable.find(*CommandPos);	           
           
	   if (CommandLookUp != BeverageDriverTable.end())
	   {
	       *(*CommandLookUp->second());//syntax problem here
	   } 
   }
   return MessageOut;
}

tried
*(*(CommandLookUp->second)());

MessageOut is a private member of the class. Really it is acting as a kind of local global variable which may be kind of ify in terms of incapsulation but I could not figure out a way to implement my DriverTable with function pointers with all different signatures.

I can't really remember my reasoning for using a pointer to a vector instead of a refrence It just was more natural for me.

Same with the string * I am passing by refrence to avoid calls to the copy constructor.

After I complete this assignment I may go back and change the types to refrences to simplify some of the coding.

I get the following error with your suggestion
/home/curlious/assignment7/src/userinterface.cpp:72: error: must use .* or ->* to call pointer-to-member function in `(&CommandLookUp)->std::_Rb_tree_iterator<_Tp>::operator-> [with _Tp = std::pair<string* const, void (BeverageUserInterface::*)()>]()->std::pair<string* const, void (BeverageUserInterface::*)()>::second (...)'

My attempt gave this error.
/home/curlious/assignment7/src/userinterface.cpp:72: error: must use .* or ->* to call pointer-to-member function in `(&CommandLookUp)->std::_Rb_tree_iterator<_Tp>::operator-> [with _Tp = std::pair<string* const, void (BeverageUserInterface::*)()>]()->std::pair<string* const, void (BeverageUserInterface::*)()>::second (...)'

Well by passing a pointer to a vector you have only caused yourself more headache (since you have to deference it). Using a string * might save you the copy constructor call but thats about all. But the complexity of the result code does not warrent such an action.

Also both errors you posted appear to be the same.

This is just a guess based off of the cryptic error:

Code:

*((*CommandLookUp)->second());

It looks like changing everything to refrences at this point is going to be very difficult. I made a quick attempt and it broke my code fiercly.

It might be difficult but it'll be worth it

Ok so I am attempting to make the change in small steps here is what I have done.

Code:

vector<string*> * BeverageUserInterface::ParseMessage(vector<string*>& MessageIn)
{
   vector<string *>::iterator CommandPos;
   BeverageDriverMap::iterator CommandLookUp;
   
   for (CommandPos = (*MessageIn).begin(); CommandPos != (*MessageIn).end(); ++CommandPos)
   {
   	   CommandLookUp = BeverageDriverTable.find(*CommandPos);	           
           
	   if (CommandLookUp != BeverageDriverTable.end())
	   {
	       *(*(CommandLookUp->second)());
	   } 
   }
   return MessageOut;
}

I get the same error:
/home/curlious/assignment7/src/userinterface.cpp:72: error: must use .* or ->* to call pointer-to-member function in `(&CommandLookUp)->std::_Rb_tree_iterator<_Tp>::operator-> [with _Tp = std::pair<string* const, void (BeverageUserInterface::*)()>]()->std::pair<string* const, void (BeverageUserInterface::*)()>::second (...)'


Also in main I am not sure how to convert to refrences as I must initialize the refrence to the vector

Code:

#include "userinterface.h"
 #include "BeerLogic.h"
 #include "ourstr.h"
 #include <vector>
 using std::vector;
int main(int argc, char * argv[])
{
  
    BeverageUserInterface MyBeverageInterface;
    BeerLogic MyBeverageLogic;
    vector<string*> * UIMessageIn;
    vector<string*> * UIMessageOut;//if I change this to vector<string *>& UIMessageOut how do I initialize it?
    const string QUIT="8";        
    do
    {  
       (*UIMessageOut).clear();
       (*UIMessageOut).push_back(new string("ShowMenu"));
       (*UIMessageOut).push_back(new string("GetMenuItem"));
       
       
       UIMessageIn = MyBeverageInterface.ParseMessage(*UIMessageOut);
       UIMessageOut = MyBeverageLogic.PerformOption(UIMessageIn);
       MyBeverageInterface.ParseMessage(*UIMessageOut);    
    }while (*(*UIMessageIn)[0] != "QUIT");
       
    return EXIT_SUCCESS;
}

Ok heres a quicky example:

Code:

#include <iostream>
#include <vector>
#include <string>
using namespace std;
void foo (vector<string>& vs)
{
  for (vector<string>::iterator bar = vs.begin();
         bar != vs.end();
         bar++
        )
    cout<<bar<<endl;

}

int main()
{
  vector<string> vStr;  // I have an object called vStr that is a vector of strings

  vStr.push_back("Hello World!");
  vStr.push_back("How are you doing today?");
  vStr.push_back("I'm doing good, finals are here.");
  vStr.push_back("Cool.");

  foo(vStr);
}

Hope that helps shows you how to use references

Oh as for your program. Where is

Code:

vector<string*> * UIMessageOut;

being assigned a memory location that has been allocated for a vector<string*>?

good point I did not initialize UIMessageIn and Out in main.
I have changed this.
If I do not use a pointer I must use a refrence for UIMessage
because it would be impractical to pass the entire vector back as a return type
so I can not simply declare
vector<string *> UIMessage;
because BeerLogic returns a pointer (at the moment -> to be refrence)
to a Messagevector

so my question stands concerning initializing the refrence to the vector in main
here is the code at the moment.

Code:

#include "userinterface.h"
 #include "BeerLogic.h"
 #include "ourstr.h"
 #include <vector>
 using std::vector;
int main(int argc, char * argv[])
{
  
    BeverageUserInterface MyBeverageInterface;
    BeerLogic MyBeverageLogic;
    vector<string*> * UIMessageIn = new vector<string *>;
    vector<string*> * UIMessageOut= new vector<string *>;
    const string QUIT="8";        
    do
    {  
       (*UIMessageOut).clear();
       (*UIMessageOut).push_back(new string("ShowMenu"));
       (*UIMessageOut).push_back(new string("GetMenuItem"));
       
       
       UIMessageIn = MyBeverageInterface.ParseMessage(*UIMessageOut);
       UIMessageOut = MyBeverageLogic.PerformOption(*UIMessageIn);
       MyBeverageInterface.ParseMessage(*UIMessageOut);    
    }while (*(*UIMessageIn)[0] != "QUIT");
       
    return EXIT_SUCCESS;
}

I want to change the pointers to refrences for UIMessages but still do not know how to init the refrence to a vector.

Code:

vector<string*> * BeverageUserInterface::ParseMessage(vector<string*>& MessageIn)
{
   vector<string *>::iterator CommandPos;
   BeverageDriverMap::iterator CommandLookUp;
   
   for (CommandPos = MessageIn.begin(); CommandPos != MessageIn.end(); ++CommandPos)
   {
   	   CommandLookUp = BeverageDriverTable.find(*CommandPos);	           
           
	   if (CommandLookUp != BeverageDriverTable.end())
	   {
	       *(*(CommandLookUp->second)());
	   } 
   }
   return MessageOut;
}

fixed the initialization of the iterator taking into account the refrence
trying to derefrence the pointer to a function refered to by CommandLookUp->second is still a problem
/home/curlious/assignment7/src/userinterface.cpp:72: error: must use .* or ->* to call pointer-to-member function in `(&CommandLookUp)->std::_Rb_tree_iterator<_Tp>::operator-> [with _Tp = std::pair<string* const, void (BeverageUserInterface::*)()>]()->std::pair<string* const, void (BeverageUserInterface::*)()>::second (...)'