Nested Loop that may potentially delete iterators of inner & outer vectors

[M.Richard Tober]

Heya all, long time no see. Anyhow, I've got a situation where a vector of sprites* is checked against another vector of sprites*. If the pair being checked intersect, I'd like to delete them both. I can handle single-delete passes, but can't wrap my head around double-deletes, since the outer loop's iterator would also need to be incremented, but only if the inner iterator was incremented... anyhow, it's kicking my butt in practice.

In the mean time, I simply set the sprite's lifetime to zero, so on the next loop, a different iteration catches and deletes the sprite.

for ( auto target = EnemyBullets.begin(); target != EnemyBullets.end(); ++target ) {
    for ( auto shot = Bullets.begin(); shot != Bullets.end(); ++shot ) {
        if (( *target )->getGlobalBounds().intersects(( *shot )->getGlobalBounds())) {
            ( *target )->setLifeTime( 0 );
            ( *shot )->setLifeTime( 0 );
        }
    }
}

The above works, but optimally first, I'd like to delete the two sprites directly. All my attempts segfault so far. Something like:

for (auto shot = Bullets.begin(); shot != Bullets.end(); ++shot) {
    for (auto target = EnemyBullets.begin(); target != EnemyBullets.end();) {
        if((*shot)->getGlobalBounds().intersects((*target)->getGlobalBounds())) {
            delete *shot;
            delete *target;
            shot = Bullets.erase(shot);
            target = EnemyBullets.erase(target);
        } else {
            ++target;
        }
    }
}

If I figure it out, I'll post an update.

[M.Richard Tober]

Well, it's a little hacky, but here's the finished solution:

            // Beginning of the code for bullet on bullet collisions.
            auto playerShotIter = PlayerBullets.begin();
            auto enemyShotIter = EnemyBullets.begin();
            bool bulletOnBulletCollision = false;

            while (playerShotIter != PlayerBullets.end())
            {
                enemyShotIter = EnemyBullets.begin();
                while (enemyShotIter != EnemyBullets.end())
                {
                    if ((*playerShotIter)->getGlobalBounds().intersects((*enemyShotIter)->getGlobalBounds())) {
                        bulletOnBulletCollision = true;
                        delete *playerShotIter;
                        delete *enemyShotIter;
                        playerShotIter = PlayerBullets.erase( playerShotIter );
                        EnemyBullets.erase( enemyShotIter );
                        enemyShotIter = EnemyBullets.end();
                    } else {
                        ++enemyShotIter;
                    }
                }
                if (bulletOnBulletCollision) {
                    bulletOnBulletCollision = false;
                } else {
                    ++playerShotIter;
                }
            }
            // End of the code for bullet on bullet collisions.

You can see I had to use an external flag (bulletOnBullerCollision) to signal to the outer loop that the outer iterator had already been incremented in an inner-loop deletion. Thanks for your time!

Any comments, questions, suggestions or improvements are welcome! Please! =D