shared_ptr and "<"

a shared_ptr implements some comparison operators
- e.g., a shared_ptr implements the “<“ operator
- but, it doesn’t invoke “<“ on the pointed-to objects
‣ instead, it just promises a stable, strict ordering
‣ given two shared pointers, it will pick some ordering between them
(probably based on the pointer address, not the pointed-to value)
- this means you can use shared_ptrs as keys in maps, but you
have to use a slightly more complex form of the sort algorithm

‣ you have to provide sort with a comparison function

bool sortfunction(shared_ptr<int> x, shared_ptr<int> y) {
 return *x < *y;
}
bool printfunction(shared_ptr<int> x) {
 std::cout << *x << std::endl;
}
int main(int argc, char **argv) {
 vector<shared_ptr<int> > vec;
 vec.push_back(shared_ptr<int>(new int(9)));
 vec.push_back(shared_ptr<int>(new int(5)));
 vec.push_back(shared_ptr<int>(new int(7)));
 std::sort(vec.begin(), vec.end(), &sortfunction);
 std::for_each(vec.begin(), vec.end(), &printfunction);
 return EXIT_SUCCESS;
}