How to copy a certain number of chars from a file to a vector the STL-way?

If I want to copy the contents of a file to a vector, I can do it like that:

std::ifstream file("path_to_file");
std::vector buffer(std::istream_iterator(file), 
                         std::istream_iterator());

My question is, how would I do this if I want to copy only the first n chars?

Edit I could write my own version of copy, but is there a way to do this using only existing components?