How to randomly position a push_back()ed sprite from a list - SFML?

How to randomly position a push_back()ed sprite from a list - SFML?

I am making this space based shooter using SFML and MS Visual Studio 10 in
C++. So, my enemy sprites are declared in a std::list. In order to keep
them coming indefinitely, I used a large size for the list. But, this
affects performance and will eventually terminate after a period of time.
So, instead I opted to push_back() an element into the list every time I
erase an element, so as to keep the size of the list constant and spawn
enemies indefinite number of times. This does not affect performance.
However, every time an enemy sprite is erased, a new sprite is being
generated at position (0,0) i.e. top left corner. So, in order to randomly
generate their positions off-screen, I used the same RNG I used to
initialize their positions at the start of the program. Now, they are
being randomly generated off-screen but the whole list is being erased and
a new list is being generated again. Here's my code:
std::list<sf::Sprite>::iterator enemyit = enemy.begin(), next;
while(enemyit != enemy.end())
{
next = enemyit;
next++;
if(enemyit->getGlobalBounds().intersects(player.getGlobalBounds()))
{
enemy.erase(enemyit);
enemy.push_back(sf::Sprite(enemytex));
srand(time(NULL));
float y = -200;
for(std::list<sf::Sprite>::iterator enemyit = enemy.begin();
enemyit != enemy.end(); enemyit++)
{
float x = rand() % dist + wastage;
enemyit->setPosition(x, y);
y = y - enemyit->getGlobalBounds().height * 2;
}
}
enemyit = next;
}
Obviously, it's the for loop. I am iterating the whole list. How do I
change it so that only one element is generated when only one is erased?
What is the condition I should set? I've tried everything to the best of
my knowledge, but nothing. Please help me on this.