Issues dynamic allocation of classes - c++

Question

I am currently trying to refresh my c++ skills with implementing a snake-game. I have created following class - relevant code snippet:
snake_class.h
#include <string>
#include <vector>
#include <windows.h>
typedef struct coordinates {
int x;
int y;
};
class Snake {
public:
std::vector<coordinates> body;
Snake(const int MAX_HEIGHT, const int MAX_WIDTH, const int initLengthSnake);
void updateSnakeBody(coordinates newDirection, int startingPoint);
};
... and with the corresponding code snippet of the .cpp-file:
snake_class.cpp
#include <vector>
#include "snake_class.h"
Snake::Snake(const int MAX_HEIGHT, const int MAX_WIDTH, const int initLengthSnake) {
for (int snakeLength = 0; snakeLength < initLengthSnake; snakeLength++) {
coordinates currentBodyPoint = { (MAX_WIDTH + initLengthSnake) / 2 - snakeLength, (MAX_HEIGHT) / 2 };
body.push_back(currentBodyPoint);
}
}
void Snake::updateSnakeBody(coordinates newDirection, int startingPoint) {
coordinates currentBodyPoint = body[startingPoint];
body[startingPoint].x += newDirection.x;
body[startingPoint].y += newDirection.y;
if (startingPoint + 1 < body.size()) {
coordinates nextDirection = { currentBodyPoint.x - body[startingPoint + 1].x,
currentBodyPoint.y - body[startingPoint + 1].y };
updateSnakeBody(nextDirection, startingPoint + 1);
}
}
My main-method looks like the following:
bool crashed = false;
int main()
{
//init-part for windows and snake length
const int windowHeight = 20;
const int windowWidth = 25;
const int initSnakeLength = 4;
//init part for snake game to move and some stock variables
coordinates direction = { 1, 0 };
bool initNeeded = false;
//snake init
Snake* snake = new Snake(windowWidth, windowHeight, initSnakeLength);
while (true) {
if (initNeeded) {
crashed = false;
Snake* snake = new Snake(windowWidth, windowHeight, initSnakeLength);
initNeeded = false;
}
if (!crashed) {
(*snake).updateSnakeBody(direction, 0);
crashed = true;
}
else {
delete snake;
initNeeded = true;
}
}
return 0;
}
Build is successfull and the first round of the game works as expected. When I feedback to the game, that I want to play another round, then the new snake class is constructed once again inside the if (initNeeded) {...}-condition. The vector also got the size of 4 after the construction.
But as soon as the program enters the line
(*snake).updateSnakeBody(direction, 0);
I retrieve the error-message vector subsrictp out of range and somehow the vector got the size 0.
I know, that I do not need to dynamically allocate a new class for getting the game to run as intended, but I wanted to try it out in this way.
I cannot really figure out why the new class behaves like that and hope some of you could help me resolving that issue!
Thanks in advance!

Answer 1

You construct two different snakes, one in the main scope, on in the scope of the if statement. Then you create two pointers to these, with the same name. You need to sort this out!
while (true) {
if (initNeeded) {
crashed = false;
Snake* snake = new Snake(windowWidth, windowHeight, initSnakeLength);
initNeeded = false;
}
This snake pointer cannot be accessed from anywhere else. Whatever you are trying to do, this must be wrong.
Perhaps this is what you meant to do
//declare snake pointer
Snake* snake;
while (true) {
if (initNeeded) {
crashed = false;
// set pointer to a new snake
snake = new Snake(windowWidth, windowHeight, initSnakeLength);
initNeeded = false;
}