How to fix 'Expression: vector subscript out of range' error

Question

I'm in the process of making a simple game via SFML and have encountered the following error:

Debug assertation failed! Expression: vector subscript out of range

This error only appears when the 'rocket' makes contact with the first 'enemy' whilst there are 3 enemies on screen at the same time.

    for (int i = 0; i < rockets.size(); i++) //This is where the error points to
    {
        for (int j = 0; j < enemies.size(); j++)
        {
            Rocket *rocket = rockets[i];
            Enemy *enemy = enemies[j];

            if (checkCollision(rocket->getSprite(), enemy->getSprite()))
            {
                //hitSound.play();
                score++;
                std::string finalScore = "Score: " + std::to_string(score);
                scoreText.setString(finalScore);
                sf::FloatRect scoreBounds = scoreText.getGlobalBounds();
                scoreText.setOrigin(scoreBounds.width / 2, scoreBounds.height / 2);
                scoreText.setPosition(viewSize.x * 0.5f, viewSize.y * 0.10f);



                rockets.erase(rockets.begin() + i);
                enemies.erase(enemies.begin() + j);

                delete(rocket);
                delete(enemy);
                if (score % 5 == 0) levelUp();
                printf("rocket intersects with enemy \n");
            }
        }
    }

I have stored the enemy and rocket objects in vectors:

    std::vector <Enemy*> enemies;
    std::vector <Rocket*> rockets;

Here's my entire update function if that helps:

void update(float dt)
{
    hero.update(dt);

    currentTime += dt;
    if (currentTime >= prevTime + 1.125f)
    {
        spawnEnemy();
        prevTime = currentTime;
    }

    for (int i = 0; i < enemies.size(); i++)
    {
        Enemy *enemy = enemies[i];
        enemy->update(dt);

        if (enemy->getSprite().getPosition().x < 0)
        {
            enemies.erase(enemies.begin() + i);
            delete(enemy);
            gameOver = true;
            gameOverSound.play();
        }
    }

    for (int i = 0; i < rockets.size(); i++)
    {
        Rocket *rocket = rockets[i];

        rocket->update(dt);

        if (rocket->getSprite().getPosition().x > viewSize.x)
        {
            rockets.erase(rockets.begin() + i);
            delete(rocket);
        }
    }

    for (int i = 0; i < rockets.size(); i++)
    {
        for (int j = 0; j < enemies.size(); j++)
        {
            Rocket *rocket = rockets[i];
            Enemy *enemy = enemies[j];

            if (checkCollision(rocket->getSprite(), enemy->getSprite()))
            {
            //hitSound.play();
                score++;
                std::string finalScore = "Score: " + std::to_string(score);
                scoreText.setString(finalScore);
                sf::FloatRect scoreBounds = scoreText.getGlobalBounds();
                scoreText.setOrigin(scoreBounds.width / 2, scoreBounds.height / 2);
                scoreText.setPosition(viewSize.x * 0.5f, viewSize.y * 0.10f);



                rockets.erase(rockets.begin() + i);
                enemies.erase(enemies.begin() + j);

                delete(rocket);
                delete(enemy);
                if (score % 5 == 0) levelUp();
                printf("rocket intersects with enemy \n");
            }
        }
    }

    for (int i = 0; i < enemies.size(); i++)
    {
        Enemy *enemy = enemies[i];

        if (checkCollision(enemy->getSprite(), hero.getSprite()))
        {
            gameOver = true;
            gameOverSound.play();
        }
    }
}

Answer 1

You can't remove elements from a vector as you iterate over it. You're removing elements but not properly adjusting i and j so you end up out of bounds with your indices.