How to remove the first N lines of a std::istream (e.g. std::stringstream)?

Question

I have a std::stringstream and I want a stringstream where the first N lines are removed. How can I achieve this?

The following lines using getline do not work as wished.

std::stringstream source(...);
for (int i(0); i < N; +i)
{
    char* c;
    source.getline(c, 256);
}
std::stringstream target(source.str());