Objects in std::vector not saving attributes correctly - c++

Question

The problem I'm having is that when I change an attribute of an Object the change isn't 'saving'. Easier to show you what's happening.
I'm learning c++ and decided to build a small chess app. Each Piece is a seperate Object.
They're stored in a std::vector as such
std::vector<Piece> pieces;
They're initialised like so
for (int i = 0; i < 2; i++)
{
Piece p;
p.Init(i*2+1, 1, renderer, SQUARE_SIZE, "king");
pieces.push_back(p);
}
When I click the mouse I want to select all pieces (temporarily)
for (int i = 0; i < pieces.size(); i++)
{
Piece p = pieces[i];
p.Select();
}
The issue is that while the Select() function is being called, by the time I get to rendering their selected attribute is false. Strangely this does not happen to the piece not contained within in the vector, referred to as k.
Before you ask there is nowhere in my code that I set selected to false :) (Except the constructor :P )
Also if you feel like downvoting, send me a comment first and I'll try fix whatever it is!
Here are the entire files. (not sure if this is the proper way to insert them)
Piece.h
#include <iostream>
#include <SDL2/SDL.h>
#include <SDL2/SDl_image.h>
#include <array>
#include <vector>
class Piece
{
public:
Piece();
void Init(int _x, int _y, SDL_Renderer* renderer, int SQUARE_SIZE, std::string type);
void SetPos(int _x, int _y, int _w);
void LoadTexture(SDL_Renderer* renderer, std::string type);
void LoadMovementVector(std::string type);
void Render(SDL_Renderer* renderer);
void Select(){ selected = true; std::cout << "called\n";}
bool isSelected(){ return selected; }
int GetX(){ return x; } // SDL_Point
int GetY(){ return y; }
private:
int x, y;
std::vector<int> move_vector;
bool selected;
SDL_Rect rect;
SDL_Texture* texture;
};
Piece.cpp
#include <iostream>
#include <SDL2/SDL.h>
#include <SDL2/SDl_image.h>
#include <vector>
#include "Piece.h"
Piece::Piece()
: x(0)
, y(0)
, selected(false)
{
}
void Piece::Init(int _x, int _y, SDL_Renderer* renderer, int SQUARE_SIZE, std::string type)
{
SetPos(_x, _y, SQUARE_SIZE);
LoadTexture(renderer, type);
LoadMovementVector(type);
}
void Piece::Render(SDL_Renderer* renderer)
{
//selected = true;
//std::cout << selected << std::endl;
if (selected)
{
SDL_SetRenderDrawColor(renderer, 255, 0, 0, 255);
SDL_RenderFillRect(renderer, &rect);
}
if (texture != nullptr)
{
SDL_RenderCopy(renderer, texture, nullptr, &rect);
}
else
{
SDL_SetRenderDrawColor(renderer, 255, 0, 0, 255);
SDL_RenderFillRect(renderer, &rect);
}
}
void Piece::LoadMovementVector(std::string type)
{
if (type == "king"){ // There literally has to be a better way to init std::vector
int arr[4] = {1,1,1,0};
for (int i = 0; i < 4; i++){ move_vector.push_back(arr[i]); }
}
for (int i = 0; i < move_vector.size(); i++)
{
std::cout << move_vector[i];
}
std::cout << std::endl;
}
void Piece::LoadTexture(SDL_Renderer* renderer, std::string type)
{
std::string source;
if (type == "king"){
source = "wk.png";
}
texture = IMG_LoadTexture(renderer, "res/wk.png");
}
void Piece::SetPos(int _x, int _y, int _w)
{
x = _x;
y = _y;
rect.x = _w*(_x-1);
rect.y = _w*(8-_y);
rect.w = _w;
rect.h = _w;
std::cout << x << y << std::endl;
}
Main.cpp
#include <iostream>
#include <math.h>
#include <SDL2/SDL.h>
#include <SDL2/SDl_image.h>
#include "Piece.h"
using namespace std::chrono;
// Would be 'const int' but I want to make the board resizeable
int SCREEN_WIDTH = 800;
int SCREEN_HEIGHT = 800;
int BOARD_WIDTH, BOARD_HEIGHT, SQUARE_SIZE;
SDL_Window* window;
SDL_Renderer* renderer;
std::vector<Piece> pieces;
Piece k;
bool InitEverything();
bool InitSDL();
bool CreateWindow();
bool CreateRenderer();
void SetupRenderer();
void Quit();
void RunGame();
void Render();
void HandleInput();
void UpdateDimensions();
double GetDelta();
void RenderGameBoard();
bool loop = true;
auto timePrev = high_resolution_clock::now();
int main(int argc, char* args[])
{
if (!InitEverything())
return -1;
std::cout << "Running Game..." << std::endl;
for (int i = 0; i < 2; i++)
{
Piece p;
p.Init(i*2+1, 1, renderer, SQUARE_SIZE, "king");
pieces.push_back(p);
}
k.Init(5, 1, renderer, SQUARE_SIZE, "king");
RunGame();
Quit();
return 0;
}
void RunGame()
{
while (loop)
{
HandleInput();
Render();
double delta = GetDelta();
}
}
void Render()
{
SDL_SetRenderDrawColor(renderer, 255, 255, 255, 255);
SDL_RenderClear(renderer);
RenderGameBoard();
for (int i = 0; i < pieces.size(); i++)
{
pieces[i].Render(renderer);
}
k.Render(renderer);
SDL_RenderPresent(renderer);
}
void RenderGameBoard()
{
for (int i = 0; i < 8; i++)
{
for (int j = 0; j < 8; j++)
{
if ((j%2==0&&i%2==0)||(j%2!=0&&i%2!=0))
SDL_SetRenderDrawColor(renderer, 255, 255, 255, 255);
else
SDL_SetRenderDrawColor(renderer, 180, 180, 180, 255);
SDL_Rect r = {i*SQUARE_SIZE, j*SQUARE_SIZE, SQUARE_SIZE, SQUARE_SIZE};
SDL_RenderFillRect(renderer, &r);
}
}
}
void HandleInput()
{
SDL_Event event;
while (SDL_PollEvent(&event))
{
if (event.type == SDL_QUIT)
loop = false;
else if (event.type == SDL_KEYDOWN)
{
}
else if (event.type == SDL_MOUSEBUTTONDOWN)
{
if (event.button.button == SDL_BUTTON_LEFT)
{
k.Select();
for (int i = 0; i < pieces.size(); i++)
{
Piece p = pieces[i];
p.Select();
}
int x = floor(event.button.x/SQUARE_SIZE)+1;
int y = 8-floor(event.button.y/SQUARE_SIZE);
for (int i = 0; i < pieces.size(); i++)
{
Piece p = pieces[i];
if (p.GetX() == x && p.GetY() == y)
{
p.Select();
}
}
}
}
}
}
void UpdateDimensions()
{
BOARD_WIDTH = SCREEN_WIDTH;
BOARD_HEIGHT = SCREEN_HEIGHT;
SQUARE_SIZE = BOARD_WIDTH/8;
}
double GetDelta()
{
auto timeCurrent = high_resolution_clock::now();
auto timeDiff = duration_cast< nanoseconds >( timeCurrent - timePrev );
double delta = timeDiff.count();
delta /= 1000000000;
timePrev = timeCurrent;
return delta;
}
bool InitEverything()
{
if (!InitSDL())
return false;
if (!CreateWindow())
return false;
if (!CreateRenderer())
return false;
SetupRenderer();
UpdateDimensions();
return true;
}
bool InitSDL()
{
if (SDL_Init(SDL_INIT_EVERYTHING) < 0)
{
std::cout << "SDL failed to initialize : " << SDL_GetError() << std::endl;
return false;
}
return true;
}
bool CreateWindow()
{
window = SDL_CreateWindow("Chess", SDL_WINDOWPOS_CENTERED, SDL_WINDOWPOS_CENTERED, SCREEN_WIDTH, SCREEN_HEIGHT, SDL_WINDOW_SHOWN);
if (!window)
{
std::cout << "Failed to create window : " << SDL_GetError() << std::endl;
return false;
}
return true;
}
bool CreateRenderer()
{
renderer = SDL_CreateRenderer(window, -1, SDL_RENDERER_ACCELERATED);
if (!renderer)
{
std::cout << "Failed to create renderer : " << SDL_GetError() << std::endl;
return false;
}
return true;
}
void SetupRenderer()
{
SDL_RenderSetLogicalSize(renderer, SCREEN_WIDTH, SCREEN_HEIGHT);
}
void Quit()
{
SDL_DestroyWindow(window);
SDL_Quit();
}

Answer 1

This:
Piece p = pieces[i];
is creating a copy of the piece at index i in the vector.
Any methods you call after that are operating on the copy, not on the piece in the array.
Instead, take a reference to it:
Piece& p = pieces[i];
After that, p is a reference to element i in the vector and any operations you perform on it are performed on the vector element.