Thread: The proper way to do a vector of objects

I've been really busy but managed to get in enough down time to learn somewhat decent info about vectors. Anyways originally my program created a dynamic array of pointers to class objects and I came across a few problems because of this. Apparently an array of pointers is now outta of the question and I will now be switching to a vector of objects instead.

In case anyone is wondering why I want a list of objects instead of pointers this little comment should clear things up.

You assumed wrong. tiles[i]->show() dereferences tiles[i] (i.e. accesses whatever it points at) before calling the show() method. That is undefined behaviour. Once undefined behaviour occurs, there is no recovery, and there is nothing the show() method (or any subsequently called function for that matter) can do to recover (short of invoking their own forms of undefined behaviour - compiler specific hacks, etc). Even if the show() method initialises the object correctly, it cannot change the pointer tiles[i] which is in a different scope (within main()).

What I'm trying to do is create a vector of already intialized objects so that I can use a conditional statement of every single element to properply layer my games art resources. This should also automatically fix a mild unrelated collision dectection problem too but first thing first layering.

You may find this interesting: https://www.youtube.com/watch?v=TC9zhufV_Z8
I assume you want to use polymorphism, so you'd be using std::vector<std::unique_ptr<ResourceBaseClass>> or std::vector<std::shared_ptr<ResourceBaseClass>>. You create the objects and push them into the vector. I don't know the reference to where you got that reply, so it seems out of place. Need more context to determine what you did wrong.
Anyway, see the video for more information on how to do game design with C++.

I don't think I'm trying to do polymorphism. Aren't dynamic arrays suppose to be similar to vectors? Well I had a problem a while ago with a dynamic array only applying the results of a conditional statement from the last element to the whole array. With a vector wouldn't I be able to apply my condition to each element individually?

Anyways I needed time to figure out how to print my code to site. I wanted to make sure it was eligible and pasting to notepad and then to the site seems to have did the trick.


Main function

Code:

#include "global.h"
#include "Function.h"
#include <iostream>
#include <vector>
#include <fstream>
#include <stdlib.h>
#include <stdio.h>
#include "SDL.h"
#include "SDL_image.h"
#include "Tile.h"
#include "Move.h"
#include "Timer.h"
#include "constant.h"








int main( int argc, char* args[] ) 
{ 


     //Quit flag 
     bool quit = false; 
 
     //The dot 
     Move character; 


     //The tiles that will be used 
     Tile *tiles[ TOTAL_TILES ]; 
     
     //The beginning of creating the vector
     std::vector <SideTile> walls; 




     //The frame rate regulator 
     Timer delta; 


     //Initialize SDL 
     if( init() == false ) 
     { 
        return 1; 
     } 


     //Load the files 
     if( load_files() == false ) 
     { 
        return 1; 
     } 


     //Clip the tile sheet 
     clip_tiles(); 
     clips_ys();


     //Set the tiles. Where the vector should be created
     if( set_tiles( tiles, walls) == false ) 
     { 
        return 1; 
     } 


 //While the user hasn't quit 
 while( quit == false ) 
 { 
    //While there's events to handle 
    while( SDL_PollEvent( &event ) ) 
    { 
        //Handle events for the dot 
        character.attack_input();
        character.handle_input(); 
    
        //If the user has Xed out the window 
        if( event.type == SDL_QUIT ) 
        { 
            //Quit the program 
            quit = true; 
        } 
    } 


     //Move the dot 
     character.move( tiles,walls, delta.get_ticks() ); 
     character.attack(delta.get_ticks());
 
    //Restart delta timer 
     delta.start(); 


     //Set the camera 
     character.set_camera(); 


    
    //Show the tiles
    for( int t = 0; t < TOTAL_TILES; t++ ) 
    { 
        tiles[ t ]->show(); 
    } 
    


    character.layer_maintance(tiles,walls);


        
    
    //Update the screen 
    if( SDL_Flip( screen ) == -1 ) 
    { 
        return 1; 
    } 


        
    
    
 }
  


 //Clean up 
 clean_up( tiles, walls ); 


 return 0; 
 }

Set tiles function where I'm trying to make the vector

Code:

bool set_tiles( Tile *tiles[], vector <SideTile>& walls) 
 { 
    //The tile offsets 
    int x = 0, y = 0; 
    int a = 0, b = 0; 
    int p = 0, q = 0; 
    int c = 0, d = 0;
    int z = 0;




    //Open the map 
    std::ifstream map( "lazy.map" ); 
    std::ifstream map2( "Zrender.map" ); 
    std::ifstream lv_1acoords ("lv1_aCoords.map"); 
    std::ifstream lv_1zcoords ("lv1_zCoords.map"); 
    std::ifstream lv_1xcoords ("lv1_xCoords.map"); 
    //If the map couldn't be loaded 
    if( map == NULL ) 
    { 
        return false; 
    } 
    if( map2 == NULL ) 
    { 
        return false; 
    } 
     //Initialize the tiles     
     for( int t = 0; t < TOTAL_TILES; t++ ) 
    { 
    //Determines what kind of tile will be made 
        int tileType = -1; 


    //Read tile from map file 
     map >> tileType; 


    //If the was a problem in reading the map 
    if( map.fail() == true ) 
    { 
        //Stop loading map 
        map.close(); 
        return false; 
    } 


    //If the number is a valid tile number 
    if( ( tileType >= 0 ) && ( tileType < TILE_SPRITES ) ) 
    { 
        tiles[ t ] = new Tile(NULL, NULL, NULL , NULL, x, y, tileType ); 
        //Move to next tile spot 
        x += TILE_WIDTH; 


    } 


    //If we don't recognize the tile type 
    else 
    { 
        //Stop loading map 
        map.close(); 
        return false; 
    } 






    //If we've gone too far 
    if( x >= LEVEL_WIDTH ) 
    { 
        //Move back 
        x = 0; 


        //Move to the next row 
        y += TILE_HEIGHT; 
    } 
 } 
 //Ending of for loop
 for( int s = 0; s < TOTAL_TILES_WALL; s++ ) 
 { 


 //Determines what kind of tile will be made 
 int tileTypeWall = -1; 
 int aPosition = -1, zPosition = -1, xPosition = -1; 


 //Read tile from map file 
 map2 >> tileTypeWall; 
 lv_1acoords >> aPosition; 
 lv_1zcoords >> zPosition;
 lv_1xcoords >> xPosition;
 //If the was a problem in reading the map 
    if( map2.fail() == true ) 
    { 
        //Stop loading map 
        map2.close(); 
        return false; 
    } 
    
    a = aPosition;
    z = zPosition;
    x = xPosition;
    
    //If the number is a valid tile number 
    if (( tileTypeWall <= TILE_REDCUBE_MEDIUM ) && ( tileTypeWall >= TILE_REDCUBE_LARGE ))
    { 
        SideTile newSideTile( a, b, NULL , NULL, x, z, tileTypeWall );
        walls.push_back(newSideTile);
    } 








 } 


 //Close the file 
 map.close(); 


 //If the map was loaded fine 
 return true; 
 }

Originally Posted by LAURENT*

Aren't dynamic arrays suppose to be similar to vectors?

A vector is a dynamic array encapsulated into a class with additional functions, such as begin, end, resize, size, etc, so yes, that would be an accurate statement.

Well I had a problem a while ago with a dynamic array only applying the results of a conditional statement from the last element to the whole array. With a vector wouldn't I be able to apply my condition to each element individually?

I have no idea what this means. Provide or show some example. Arrays and vectors do not differ, so it would stand to reason that you are doing something weird in your code rather than the difference between vectors and arrays.

Originally Posted by Elysia

I don't know the reference to where you got that reply, so it seems out of place.

I wrote the quoted text in another thread, where the context was along the lines of;

Code:

//   define a Tile struct/class type with a show() member
int main()
{
     Tile *tiles[20];           // uninitialised array of pointer

     // intervening code did not initialise the array

     for (int i = 0; i < 20; ++i)
        tiles[i]->show();
}

and the OP assuming nothing was wrong.

I have no idea how that extract is relevant to this thread.

Originally Posted by grumpy

I wrote the quoted text in another thread, where the context was along the lines of;

Code:

//   define a Tile struct/class type with a show() member
int main()
{
     Tile *tiles[20];           // uninitialised array of pointer

     // intervening code did not initialise the array

     for (int i = 0; i < 20; ++i)
        tiles[i]->show();
}

and the OP assuming nothing was wrong.

I have no idea how that extract is relevant to this thread.

The goal was to replace the dynamic array with a vector and to create a vector of class objects. This statement below is the sole cause of me wanting to use a vector with the belief I'll get the functionality I want.

Code:

int main()
{
     Tile *tiles[20];           // uninitialised array of pointer

     // intervening code did not initialise the array

     for (int i = 0; i < 20; ++i)
        tiles[i]->show();
}

This is my previous idea but it did not work. The last element of the array which is 20 is the only one that get's checked. When this happens the the LayerFunction returns 1 for all elements.

Code:

int main()
{
    Tile *tiles[20]; // uninitialised array of pointer


    // intervening code did not initialise the array


    for (int i = 0; i < 20; i++)
    if (layerFunction() == 1)
    {    
        //If layerFunction returns 1 show the character first. Behind
        printCharacter();
        printEfects();
        tiles[i]->show();
    }
    
    else if (layerFunction() == 2)
    {
        tiles[i]->show();
        //If layerFunction returns 2 show the last. Front
        printCharacter();
        printEfects();
    }
    
}

Originally Posted by Elysia

A vector is a dynamic array encapsulated into a class with additional functions, such as begin, end, resize, size, etc, so yes, that would be an accurate statement.



I have no idea what this means. Provide or show some example. Arrays and vectors do not differ, so it would stand to reason that you are doing something weird in your code rather than the difference between vectors and arrays.

Alright then since this is still on track with the thread. I want to create an array of initialized class objects not an array of pointer.

Originally Posted by LAURENT*

The goal was to replace the dynamic array with a vector and to create a vector of class objects. This statement below is the sole cause of me wanting to use a vector with the belief I'll get the functionality I want.

This is my previous idea but it did not work. The last element of the array which is 20 is the only one that get's checked. When this happens the the LayerFunction returns 1 for all elements.

Trying to dereference an uninitialized pointer is undefined behavior which means that anything can happen. Since I still don't know what is in LayerFunction, I still don't know why it returns 1 for everything, though.
But regardless, since you are using uninitialized pointers, it doesn't matter.

Originally Posted by LAURENT*

Alright then since this is still on track with the thread. I want to create an array of initialized class objects not an array of pointer.

Daved points out the right way. Sure remember that you will get no polymorphism if you do that, which is commonly used in game design (just check the link I gave in the first reply!).