Question

I’ve got weird problem. I’m trying to write simple game in C++, but I failed on objects and data types. There’s a code:

// C++
// Statki

#include <stdio.h>
#include <time.h>
#include <map>
#include <vector>
#include <string>
#include <list>

#define D true

using namespace std;

void _(char* message){printf("%s\n",message);};

struct relpoint { int x,y; };
struct point { int x,y; };
struct size { int w,h; };

map<const char*, vector<relpoint> > shipshape;
list<char*> shipTypes = {"XS", "S", "M", "L", "XL"};

string alpha="ABCDEFGHIJKLMNOPRSTUVWXYZ";

enum fieldtype { UNKNOWN=-1,EMPTY=0,SHIP=1,HIT=2,MISS=3,};

enum rotation { EAST=0, SOUTH=1, WEST=2, NORTH=3 };

class Ship
{
    char* type;

};

class Sea
{
    public:
    void init(size mapsize) { init( mapsize, EMPTY ); };
    void init(size mapsize, fieldtype fill)
    {
        if(D)printf("Generating sea\n");
        vector<fieldtype> v;

        seamap.reserve(mapsize.h);
        v.reserve(mapsize.w);

        for (int y=0; y<mapsize.h; y++)
        {
            v.clear();
            for(int x=0; x<mapsize.w; x++)
            {
                v.push_back(fill);
            }
            seamap.push_back(v);
        }

        view();
    };

    bool place_ship(Ship ship);

    void view()
    {
        for( vector< vector<fieldtype> >::const_iterator yy = seamap.begin(); yy != seamap.end(); ++yy )
        {
            for( vector<fieldtype>::const_iterator xx = (*yy).begin(); xx != (*yy).end(); ++xx )
            {
                if(D)printf("%d ", *xx);
            }
            if(D)printf("\n");
        }
    };

    private:
    vector< vector<fieldtype> > seamap;
};

class Game
{
    public:

    void initmap(size mapsize)
    {
        if(D) printf("\nInit %d×%d map\n", mapsize.w, mapsize.h);

        (*enemymap).init(mapsize, UNKNOWN);
        //(*selfmap).init(mapsize);
    };

    bool placeship(string type, point position, rotation rotate);
    fieldtype shoot(point target);
    void viewmap(){(*selfmap).view();};

    bool eog();

    Sea * enemymap;
    Sea * selfmap;
};

class Bot
{
    public:

    void init(size mapsize)
    {
        if(D)_("Init Bot");
    }

    private:

    Game * g;
};

class Player
{

    public:
    Player() { if(D){_("Player fake init");} };

    void init(size mapsize)
    {
        (*g).initmap(mapsize);
    };

    void viewmap(){(*g).viewmap();};

    private:
    Game * g;

};

class Router
{

    public:

    void startgame();
    void welcomescreen()
    {
        printf("\n\n\n\t\t\tShips minigame\n\t\t\t\tby Kris\n\n");

        mainmenu();
    };
    void mainmenu()
    {
        printf("Menu (type letter):\n\tN: New game\n\tS: Settings\n\tQ: Quit game\n\n > ");

        char opt;
        opt = toupper(getchar());

        size ms;

        switch(opt)
        {
            case 'N':
                ms = getmapsize();
                (*P1).init(ms);
                (*P2).init(ms);
            break;

            case 'S':

            break;

            case 'Q':

            break;

            default:
                printf("Invalid option %c", opt);
                mainmenu();
        }
    };

    private:
    Player * P1;
    Bot    * P2;

    size getmapsize()
    {
        size ms;
        printf("\nSet map size (X Y)\n > ");
        scanf("%d %d", &ms.w, &ms.h);
        return ms;
    };
};

int main () {

    vector<relpoint> shp;
    shp.reserve(5);
    list<char*>::const_iterator tp = shipTypes.begin();
    shp.push_back({0,0});
    shipshape[*(tp++)] = shp;
    shp.push_back({1,0});
    shipshape[*(tp++)] = shp;
    shp.push_back({2,0});
    shipshape[*(tp++)] = shp;
    shp.push_back({3,0});
    shipshape[*(tp++)] = shp;
    shp.push_back({2,1});
    shipshape[*tp] = shp;

    Router R;
    R.welcomescreen();

    printf("\n\n");
    return 0;
}

It can be compiled, but after line Init 5×5 map program stops with Naruszenie ochrony pamięci (Memory access violation in polish) error. Problem seems to occur at both Sea::init() functions.

I’m compiling it with g++ -std=c++0x -Wno-write-strings ships2.cpp (to prevent warnings) on Ubuntu.

Any idea what’s wrong with it?

Answer 1

You are using an uninitialized pointer. You can fix it by instantiating an object here, or in a constructor somewhere else.

Here is an example of instantiating in the initmap call.

void initmap(size mapsize)
{
    // Initialize the pointer by instantiating a class
    enemymap = new Sea;
    if(D) printf("\nInit %d×%d map\n", mapsize.w, mapsize.h);

    (*enemymap).init(mapsize, UNKNOWN);
    //(*selfmap).init(mapsize);
};