Vector init and for loop in C++11

the trick is that you need to get a reference to the object in the vector, if you do:

vector<particle> particles;

particles.resize(20); 

for ( auto p : particles) {
   p.setup(posX, posY, width, heiht);
}

you are making a copy and calling setup on that copy, if you want to modify the original in the vector the correct syntax is:

vector<particle> particles;

particles.resize(20); 

for ( auto & p : particles) {
   p.setup(posX, posY, width, heiht);
}

note the & between auto and p that makes p a reference to the object in the vector instead of a copy.