Question

I basically have exp>=level*10 in an else if expression, where level is a variable and 10 is a constant number. The code compiles completely fine without any errors, and it even worked after being compiled, until recently. now, whenever it compiles and executes, it gives me an error saying “invalid null pointer” and it conveniently tells me that the problem comes from the included file xstring (VS2010 includes it in new projects) on line 930.
Is there a way to force to program to read it as the multiplication operator instead of a null pointer?
EDIT: Here is my full code, please note that this is a protype created to ensure that it will work and was done prior to me realizing I can use derived classes for this. also note that I tried removing using namespace std to see if that was the problem.

#include "stdafx.h"
#include <iostream>
#include <sstream>

class player {
public:
    std::string name;
    int hp;
    int attack;
    int strength;
    int defense;
    void reward(int gold, int exp) {
        player::gold += gold; 
        player::exp += exp;
        player::levelHandler();
    }
    int dataQuery(std::string query) {
        if (query == "equipment")
            return helm, armour, greaves;
        else if (query == "gold")
            return gold;
        else if (query == "exp")
            return exp;
        else if (query == "level")
            return level;
        else return 0;
    }
private:
    int helm;
    int armour;
    int greaves;
    int level;
    int gold;
    int exp;
    std::string levelHandler() {
        if (level==0) { 
            level=1;
        }
        else if (exp>=(10*level)) { //causes problem due to * being mistaken as a 
                    //null pointer.
        int previousLevel = level;
        level += 1;
        levelHandler();
        return 0;
        };
        return 0;
    };
} hero;

class enemy {
public:
    std::string name;
    int hp;
    int attack;
    int strength;
    int defense;
private:
    int helm;
    int armour;
    int greaves;
    int level;
    int goldReward;
    int expReward;
    int dataQuery(std::string query) {
        if (query == "equipment")
            return helm, armour, greaves;
        else if (query == "gold")
            return goldReward;
        else if (query == "exp")
            return expReward;
        else if (query == "level")
            return level;
        else return 0;
    }
};

int main()
{
    std::cout << "Please enter your character's name..." << std::endl;
    std::cin >> hero.name;
    std::cout << "Welcome to RPG Battle Simulation, " << hero.name << "!" << std::endl;
    hero.reward(100, 0); //problem is either this line, or the function's call to levelHandler, as this is where the program terminates.
    std::cout << "You are beginning your journey as a level " << hero.dataQuery("level") << " character." << std::endl;
    std::cout << "Here is " << hero.dataQuery("gold") << " gold to get you started." << std::endl;
    return 0;
};

The following is an excerpt of xstring that is causing the problem. the problem comes from _DEBUG_POINTER(_Ptr); (line 930)

_Myt& assign(const _Elem *_Ptr)
        {// assign [_Ptr, <null>)
 _DEBUG_POINTER(_Ptr);
 return (assign(_Ptr, _Traits::length(_Ptr)));
       }

Answer 1

This program reproduces your problem (when compiled with MSVC with runtime that supports debugging):

#include <string>
#include <iostream>

int main()
{
    using namespace std;

    string  s = 0;
    cout << s << endl;
}

The problem is that a std::string is initialized with a nullpointer.

EDIT: oh, forgot to mention, solution – simply don’t do that.

Cheers & hth.,